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United States Patent | 6,078,823 |
Chavez , et al. | June 20, 2000 |
Multiple antenna cellular network
Abstract
A multiple antenna cellular network communicates with a mobile station over a plurality of antennas. The antennas are arranged in a plurality of positions to customize a cell or cells. A transceiver is coupled to the antennas and configured to receive inbound information from the mobile station and transmit outbound information to the mobile station. A processor is coupled to the transceiver and configured to decode the inbound information and to encode the outbound information to communicate with the mobile station. In another embodiment, the antennas are similarly deployed to create a cell or cells. The transmit signal power is continuously modified to improve quality and to move the nulls so that a fixed location user can receive a high quality signal. Exemplary embodiments are provided for use with the Global Systems for Mobile Communication (GSM) protocol and can be applied to other digital technologies.
Inventors: | Chavez; David A. (Monte Sereno, CA); Sayers; Ian L. (Redwood City, CA); Sage; Gerald F. (Mountain View, CA) |
Assignee: | Interwave Communications International Ltd. (Hamilton, BM) |
Appl. No.: | 582512 |
Filed: | January 3, 1996 |
Current U.S. Class: | 455/562; 370/337; 370/347; 455/101; 455/103; 455/132; 455/134; 455/422; 455/524 |
Intern'l Class: | H04B 001/40; 134; 135; 277.1; 277.2; 88 |
Field of Search: | 455/53.1,507,33.1,422,33.2,436,33.3,562,56.1,524,101,102,103,104,105,132,133 370/328,332,334,347,337 375/220,260,347 |
References Cited [Referenced By]
U.S. Patent Documents
Re34540 | Feb., 1994 | Wu et al. | 455/20. |
5023900 | Jun., 1991 | Tayloe et al. | 455/424. |
5235615 | Aug., 1993 | Omura | 375/200. |
5243598 | Sep., 1993 | Lee | 455/436. |
5363428 | Nov., 1994 | Nagashima | 379/58. |
5590404 | Dec., 1996 | Sato et al. | 455/53. |
5884173 | Mar., 1999 | Sollner | 455/436. |
Foreign Patent Documents | |||
WO 93/10619 | May., 1993 | WO | . |
WO 94/05109 | Mar., 1994 | WO | . |
Lee, "Smaller Cells for Greater Performance", IEEE 29(11):19-23 (1991). Kerpez and Ariyavisitakul, "A Radio Access System with Distributed Antennas", IEEE 3:1696-1700 (1994). |
Primary Examiner: Nguyen; Lee
Attorney, Agent or Firm: Flehr Hohbach Test Albritton & Herbert LLP
Parent Case Text
RELATED APPLICATIONS
The present application claims priority to U.S. Provisional Application No.
60/006,656, filed Nov. 13, 1995; and incorporates the following patent
applications by reference: U.S. Ser. No. 08/435,709 filed May 4, 1995; U.S. Ser.
No. 08/435,838 filed May 4, 1995, now U.S. Pat. No. 5,577,029; U.S. Ser. No.
08/434,597 filed May 4, 1995; U.S. Ser. No. 08/434,554 filed May 4, 1995, now
U.S. Pat. No. 5,682,403; and U.S. Ser. No. 08/434,598 filed on May 4, 1995.
Claims
What is claimed is:
1. A multiple antenna cellular network for communicating with a plurality of
mobile stations within a cell, comprising:
a plurality of remote transceivers each having a respective antenna and
positioned at predetermined spaced apart locations to produce the cell, said
remote transceivers configured to receive inbound information from said mobile
stations and to transmit outbound information to said mobile stations, where
each remote transceiver is configured to communicate with mobile stations in
communication proximity to said respective antenna, and where each remote
transceiver includes a receive channel having a down-converter, a received
signal strength measurement circuit configured to measure inbound information
signal strength and generate a received signal strength value, and a switch to
selectively allow or disallow transmission of said inbound information to an
output port;
a local transceiver coupled to said output port of each of said remote
transceivers and configured to receive said received signal strength value from
each of said remote transceivers, to selectively set said switch in a selected
remote transceiver based on predetermined criteria to allow said selected remote
transceiver to transmit said inbound information to said local transceiver, and
to transmit said outbound information to at least one of said remote
transceivers; and
a processor coupled to said local transceiver and to an external port and
configured to process said inbound information and outbound information to
conform said inbound information for communication with said external port and
to conform said outbound information for communication with said mobile
stations.
2. The multiple antenna cellular network of claim 1, wherein:
said local transceiver is configured to communicate substantially identical
outbound information to a multiplicity of said remote transceivers; and
said multiplicity of remote transceivers are configured to simultaneously
transmit said substantially identical outbound information.
3. The multiple antenna cellular network of claim 2, wherein:
said multiplicity of remote transceivers are configured to transmit said
substantially identical outbound information at a substantially identical
frequency; and
said multiplicity of remote transceivers are configured to periodically vary
outbound information output power to move nulls in the cell.
4. The multiple antenna cellular network of claim 1, wherein:
said local transceiver is configured to selectively set said switch in a
selected remote transceiver having a greatest received signal strength value.
5. The multiple antenna cellular network of claim 1, wherein:
said remote transceivers are configured to communicate with said mobile stations
using a time division multiple access protocol having frames including a
plurality of time slots;
said remote transceivers are configured to generate said received signal
strength value for each of said frames; and
said local transceiver is configured to selectively set said switch in a
selected remote transceiver having a greatest received signal strength value,
whereby:
(a) a remote transceiver having a greatest received signal strength value during
a first frame is configured to communicate said inbound information to said
local transceiver during a first time period; and
(b) a remote transceiver having a greatest received signal strength value during
a second frame is configured to communicate said inbound information to said
local transceiver during a second time period.
6. The multiple antenna cellular network of claim 1, wherein:
each of said remote transceivers includes an RF transceiver to communicate
information with said mobile stations and an IF transceiver coupled to said
output port to communicate IF information with said local transceiver, said IF
information including both inbound information and control information wherein
said inbound information is assigned to a set of time slots at a first IF
frequency and said control information is assigned to a set of time slots at a
second IF frequency, said control information including received signal strength
values and selective switch settings; and
said local transceiver includes an IF transceiver to communicate IF information
with said remote transceivers and an interface circuit to communicate
information with said processor.
7. The multiple antenna cellular network of claim 6, wherein:
said local transceiver is configured to communicate substantially identical
outbound information to a multiplicity of said remote transceivers; and
said multiplicity of remote transceivers are configured to simultaneously
transmit said substantially identical outbound information.
8. The multiple antenna cellular network of claim 7, wherein:
said multiplicity of remote transceivers are configured to transmit said
substantially identical outbound information at a substantially identical
frequency; and
said multiplicity of remote transceivers are configured to periodically vary
outbound information output power to move nulls in the cell.
9. The multiple antenna cellular network of claim 6, wherein:
said local transceiver is configured to selectively set said switch in a
selected remote transceiver having a greatest received signal strength value.
10. The multiple antenna cellular network of claim 6, wherein:
said remote transceivers are configured to communicate with said mobile stations
using a time division multiple access protocol having frames including a
plurality of time slots;
said remote transceivers are configured to generate said received signal
strength value for each of said frames; and
said local transceiver is configured to selectively set said switch in a
selected remote transceiver having a greatest received signal strength value,
whereby:
(a) a remote transceiver having a greatest received signal strength value during
a first frame is configured to communicate said inbound information to said
local transceiver during a first time period; and
(b) a remote transceiver having a greatest received signal strength value during
a second frame is configured to communicate said inbound information to said
local transceiver during a second time period.
11. The multiple antenna cellular network of claim 1, for further communicating
with a plurality of second mobile stations within a second cell, said network
further comprising:
a plurality of second remote transceivers each having a respective antenna and
positioned at predetermined spaced apart locations to produce the second cell,
said second remote transceivers configured to receive second inbound information
from said second mobile stations and to transmit second outbound information to
said second mobile stations, where each second remote transceiver is configured
to communicate with second mobile stations in communication proximity to said
respective antenna, and where each second remote transceiver includes a receive
channel including a down-converter, a received signal strength measurement
circuit configured to measure second inbound information signal strength and
generate a second received signal strength value, and a switch to selectively
allow or disallow transmission of said second inbound information to an output
port;
a second local transceiver coupled to said output port of each of said second
remote transceivers and configured to receive said second received signal
strength value from each of said second remote transceivers, to selectively set
said switch in a selected second remote transceiver based on predetermined
criteria to allow said selected second remote transceiver to transmit said
second inbound information to said second local transceiver, and to transmit
said second outbound information to at least one of said second remote
transceivers; and
wherein said processor is coupled to said second local transceiver and
configured to process said second inbound information and second outbound
information to conform said second inbound information for communication with
said external port and to conform said second outbound information for
communication with said second mobile stations.
12. The multiple antenna cellular network of claim 11, wherein:
said local transceiver is configured to communicate substantially identical
outbound information to a multiplicity of said remote transceivers;
said multiplicity of remote transceivers are configured to simultaneously
transmit said substantially identical outbound information;
said second local transceiver is configured to communicate substantially
identical second outbound information to a multiplicity of said second remote
transceivers; and
said multiplicity of second remote transceivers are configured to simultaneously
transmit said substantially identical second outbound information.
13. The multiple antenna cellular network of claim 12, wherein:
said multiplicity of remote transceivers are configured to transmit said
substantially identical outbound information at a substantially identical
frequency;
said multiplicity of remote transceivers are configured to periodically vary
outbound information output power to move nulls in the cell;
said multiplicity of second remote transceivers are configured to transmit said
substantially identical second outbound information at a substantially identical
frequency; and
said multiplicity of second remote transceivers are configured to periodically
vary outbound information output power to move nulls in the second cell.
14. The multiple antenna cellular network of claim 11, wherein:
said local transceiver is configured to selectively set said switch in a
selected remote transceiver having a greatest received signal strength value;
and
said second local transceiver is configured to selectively set the switch in a
selected second remote transceiver having a greatest second received signal
strength value.
15. The multiple antenna cellular network of claim 11, wherein:
said remote transceivers are configured to communicate with said mobile stations
using a time division multiple access protocol having frames including a
plurality of time slots;
said remote transceivers are configured to generate said received signal
strength value for each of said frames; and
said local transceiver is configured to selectively set the switch in a selected
remote transceiver having a greatest received signal strength value, whereby:
(a) a remote transceiver having a greatest received signal strength value during
a first frame is configured to communicate said inbound information to said
local transceiver during a first time period; and
(b) a remote transceiver having a greatest received signal strength value during
a second frame is configured to communicate said inbound information to said
local transceiver during a second time period;
said second remote transceivers are configured to communicate with said second
mobile stations using a time division multiple access protocol having frames
including a plurality of time slots;
said second remote transceivers are configured to generate said second received
signal strength value for each of said frames; and
said second local transceiver is configured to selectively set the switch in a
selected second remote transceiver having a greatest second received signal
strength value, whereby:
(a) a second remote transceiver having a greatest received signal strength value
during a first frame is configured to communicate said inbound information to
said second local transceiver during a first time period; and
(b) a second remote transceiver having a greatest received signal strength value
during a second frame is configured to communicate said inbound information to
said local transceiver during a second time period.
16. The multiple antenna cellular network of claim 11, wherein:
each of said remote transceivers includes an RF transceiver to communicate
information with said mobile stations and an IF transceiver coupled to said
output port to communicate IF information with said local transceiver, said IF
information including both inbound information and control information wherein
said inbound information is assigned to a set of time slots at a first IF
frequency and said control information is assigned to a set of time slots at a
second IF frequency, said control information including received signal strength
values and selective switch settings; and
said local transceiver includes an IF transceiver to communicate IF information
with said remote transceivers and an interface circuit to communicate
information with said processor;
each of said second remote transceivers includes an RF transceiver to
communicate information with said second mobile stations and an IF transceiver
coupled to said second output port to communicate IF information with said
second local transceiver, said IF information including both second inbound
information and second control information wherein said second inbound
information is assigned to a set of time slots at said first IF frequency and
said control information is assigned to a set of time slots at said second IF
frequency, said control information including second received signal strength
values and selective switch settings; and
said second local transceiver includes an IF transceiver to communicate IF
information with said second remote transceivers and an interface circuit to
communicate information with said processor.
17. The multiple antenna cellular network of claim 16, wherein:
said local transceiver is configured to communicate substantially identical
outbound information to a multiplicity of said remote transceivers;
said multiplicity of remote transceivers are configured to simultaneously
transmit said substantially identical outbound information;
said second local transceiver is configured to communicate substantially
identical second outbound information to a multiplicity of said second remote
transceivers; and
said multiplicity of second remote transceivers are configured to simultaneously
transmit said substantially identical second outbound information.
18. The multiple antenna cellular network of claim 17, wherein:
said multiplicity of remote transceivers are configured to transmit said
substantially identical outbound information at a substantially identical
frequency;
said multiplicity of remote transceivers are configured to periodically vary
said outbound information output power to move nulls in the cell;
said multiplicity of second remote transceivers are configured to transmit said
substantially identical second outbound information at a substantially identical
frequency; and
said multiplicity of second remote transceivers are configured to periodically
vary outbound information output power to move nulls in the second cell.
19. The multiple antenna cellular network of claim 16, wherein:
said local transceiver is configured to selectively set the switch in a selected
remote transceiver having a greatest received signal strength value; and
said second local transceiver is configured to selectively set the switch in a
selected second remote transceiver having a greatest second received signal
strength value.
20. The multiple antenna cellular network of claim 16, wherein:
said remote transceivers are configured to communicate with said mobile stations
using a time division multiple access protocol having frames including a
plurality of time slots;
said remote transceivers are configured to generate said received signal
strength value for each of said frames; and
said local transceiver is configured to selectively set the switch in a selected
remote transceiver having a greatest received signal strength value, whereby:
(a) a remote transceiver having a greatest received signal strength value during
a first frame is configured to communicate said inbound information to said
local transceiver during a first time period; and
(b) a remote transceiver having a greatest received signal strength value during
a second frame is configured to communicate said inbound information to said
local transceiver during a second time period;
said second remote transceivers are configured to communicate with said second
mobile stations using a time division multiple access protocol having frames
including a plurality of time slots;
said second remote transceivers are configured to generate said second received
signal strength value for each of said frames; and
said second local transceiver is configured to selectively set the switch in a
selected second remote transceiver having a greatest second received signal
strength value, whereby:
(a) a second remote transceiver having a greatest received signal strength value
during a first frame is configured to communicate said inbound information to
said second local transceiver during a first time period; and
(b) a second remote transceiver having a greatest received signal strength value
during a second frame is configured to communicate said inbound information to
said local transceiver during a second time period.
21. A method of communicating with a plurality of mobile stations within a cell
using a multiple antenna cellular network having a plurality of remote
transceivers each having a respective antenna and positioned at predetermined
spaced apart locations to produce the cell and configured to receive inbound
information from said mobile stations and transmit outbound information to said
mobile stations, and where each remote transceiver includes a receive channel
having a received signal strength measurement circuit configured to measure
inbound information signal strength and generate a received signal strength
value, and a switch to selectively allow or disallow transmission of said
inbound information to an output port, a local transceiver coupled to said
output of each of said remote transceivers and to a processor configured to
process said inbound information and outbound information, said method
comprising the steps of:
receiving inbound information at the remote transceivers;
measuring inbound information power levels from said mobile stations at each of
said remote transceivers and generating a received signal strength value;
communicating said received signal strength values to said local transceiver;
determining in said local transceiver a selected remote transceiver meeting a
predetermined criteria based on said received signal strength values and
transmitting to said selected remote transceiver a selective switch setting;
setting the switch in said selected remote transceiver to allow communication of
said inbound information to said local transceiver; and
transmitting said inbound information from said selected remote transceiver to
said local transceiver.
22. The method of claim 21, further comprising the steps of:
communicating substantially identical outbound information from said local
transceiver to a multiplicity of said remote transceivers;
simultaneously transmitting said substantially identical outbound information
from said multiplicity of remote transceivers at a substantially identical
frequency; and
periodically varying an outbound information output power of said remote
transceivers to move nulls in the cell.
23. The method of claim 21, wherein said remote transceivers are configured to
communicate with said mobile stations using a time division multiple access
protocol having frames including a plurality of time slots; and wherein:
said measuring step includes the steps of measuring inbound information power
levels from said mobile stations and generating said received signal strength
value for each of said frames; and
said determining step includes the step of selecting a remote transceiver having
a greatest received signal strength value, whereby:
(a) a remote transceiver having a greatest received signal strength value during
a first frame is configured to communicate said inbound information to said
local transceiver during a first time period; and
(b) a remote transceiver having a greatest received signal strength value during
a second frame is configured to communicate said inbound information to said
local transceiver during a second time period.
24. The method of claim 23, further comprising the steps of:
communicating substantially identical outbound information from said local
transceiver to a multiplicity of said remote transceivers;
simultaneously transmitting said substantially identical outbound information
from said multiplicity of remote transceivers at a substantially identical
frequency; and
periodically varying an outbound information output power of said remote
transceivers to move nulls in the cell.
Description
FIELD
The present invention relates to a multiple antenna cellular network. In
particular, the invention is used in a cellular communication network to custom
configure cell boundaries to accommodate obstacles such as walls, ceilings,
floors and buildings to reduce interference, improve performance and improve
quality of service.
BACKGROUND
Standard cellular communication networks are generally divided into geographic
cells. Each cell typically contains a central antenna, is circular and overlaps
slightly with adjacent cells. Base transceiver station hardware is deployed near
each antenna to communicate with mobile stations in that cell. Factors that
influence cellular design and the amount of deployed hardware include the number
of mobile stations to be serviced in a given area, the operational power levels
of the mobile stations and base stations, and the presence or absence of
obstacles. Other factors include the type of communication protocol such as time
division multiple access (TDMA), frequency division multiple access (FDMA), code
division multiple access (CDMA), or other type. The transmit power and the
communication protocol generally define the size of each cell and how many users
each cell can support.
When a cellular network is designed, a specified number of users can be serviced
by a specified number of cells and associated hardware including the base
transceiver stations. When a mobile station passes from one cell to another, a
hand-off is performed to permit the mobile station to communicate with the base
transceiver station that receives the strongest signal from the mobile station.
However, in some circumstances, signals are blocked by obstacles such as
buildings and mountains. To accommodate these obstacles, multipath signal
processing is performed, but it is not successful at all possible locations. To
service all locations, additional antennas or repeaters must be deployed to
create additional cells or enhance coverage even though no additional capacity
may be supported. This type of hardware deployment is not efficient.
Low power cellular networks, such as those designed to service a building, have
similar problems. In this case, the obstacles are walls, floors and ceilings. To
accommodate these obstacles, additional antennas are deployed to create
additional cells. Again, the result is that additional antenna or repeater
hardware is deployed without an associated increase in the number of serviced
mobile stations. Similarly, this deployment is not efficient.
Hence, one limitation of existing systems is that they require additional
antenna or repeater hardware to provide service to mobile stations that move
behind an obstacle. This results in a deployment of a large amount of hardware
for the purpose of communicating with a statistically small number of mobile
stations.
SUMMARY
The present invention relates to a multiple antenna cellular network. In
particular, the invention is used in a cellular communication network to custom
configure cell boundaries to accommodate obstacles such as walls, ceilings,
floors and buildings to reduce interference, improve performance and improve
quality of service. Exemplary embodiments are provided for use with the Global
Systems for Mobile Communication (GSM) protocol and can be applied to other
cellular communication and digital technologies.
A multiple antenna cellular network communicates with a mobile station over a
plurality of antennas. The antennas are arranged in a plurality of positions to
customize a cell or cells. A transceiver is coupled to the antennas and
configured to receive inbound information from the mobile station and transmit
outbound information to the mobile station. A processor is coupled to the
transceiver and configured to decode the inbound information and to encode the
outbound information to communicate with the mobile station.
In another embodiment, the antennas are similarly deployed to create a cell or
cells. The transmit signal power is continuously varied to improve quality and
to move the nulls so that a fixed location user can receive a high quality
signal.
Advantages of the invention include improved cell boundary control, reduced
interference, fault tolerance and more efficient use of radio resources.
Additionally, mobile users will experience improved battery life because of
lower mobile station transmit power requirements.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional advantages of the invention will become apparent upon reading the
following detailed description and upon reference to the drawings, in which:
FIG. 1 depicts a multiple antenna cellular network showing a customized cell,
several remote transceivers, a local transceiver and a processor according to an
embodiment of the invention;
FIG. 2 depicts the communication frequency spectrum between a remote transceiver
and a local transceiver according an to an embodiment of the invention;
FIG. 3 is a control data word communicated between a remote transceiver and a
local transceiver according to an embodiment of the invention;
FIG. 4 is a flow chart showing operation of a multiple antenna cellular network
according to an embodiment of the invention;
FIG. 5 is a schematic of a remote transceiver according to an embodiment of the
invention; and
FIG. 6 is a schematic of a local transceiver according to an embodiment of the
invention.
DETAILED DESCRIPTION
The present invention relates to a multiple antenna cellular network. In
particular, the invention is used in a cellular communication network to custom
configure cell boundaries to accommodate obstacles such as walls, ceilings,
floors and buildings to reduce interference, improve performance and improve
quality of service. Exemplary embodiments are provided for use with a TDMA
communication protocol and the Global Systems for Mobile Communication (GSM)
communication protocol and can be applied to other cellular communication and
digital technologies. An overview of GSM is described in the U.S. patent
application SPREAD SPECTRUM COMMUNICATION NETWORK WITH ADAPTIVE FREQUENCY
AGILITY, U.S. Ser. No. 08/434,597, filed on May 4, 1995.
Exemplary embodiments are described herein with reference to specific
configurations and protocols. For example, the embodiments are described as
employing non-frequency-hopping communication, but could be implemented to
frequency hop. Those skilled in the art will appreciate that various changes and
modifications can be made to the exemplary embodiments while remaining within
the scope of the present invention. The invention can be employed using any TDMA,
FDMA, CDMA or other similar communication protocol.
HARDWARE CONFIGURATION
An exemplary embodiment is described with reference to FIGS. 1 through 6. FIG. 1
is a general illustration of a multiple antenna cellular network according to an
embodiment of the invention. FIG. 1 shows two cells 115 and 119 in a building
installation. While the embodiment is explained with reference to cell 115 and
the components thereof, the explanation is equally applicable to cell 119 and
the components thereof.
A plurality of remote transceivers 112a-c are positioned at a number of
locations 114a-c to develop cell 115. Each location 114a-c represents a sub-cell
that develops cell 115. For example, remote transceivers 112a-c can be placed in
rooms or in hallways to develop cell 115. Cell 115 has a shape that is defined
by the remote transceivers 112a-c and the radiated power associated with each
remote transceiver 112a-c. In this embodiment, all the remote transceivers
112a-c have common transmit and receive cycles (explained below). This makes it
possible for a mobile station to move among sub-cells 114a-c within cell 115 and
experience continuous high quality communication.
All remote transceivers 112a-c are coupled, via data link 120a, to a local
transceiver 130a. Similarly, all remote transceivers 116a-c are coupled, via
data link 120b, to a local transceiver 130b. Data links 120a-b can be coaxial
cables, fiber-optic cables, or other type of communication medium such as RF
links. Moreover, any number of remote transceivers can be coupled to a local
transceiver. Six remote transceivers per local transceiver is a typical
configuration. This configuration permits a number of remote transceivers to be
positioned at a number of locations to provide a custom cell having any physical
space parameters. For example, the cell can be an entire building, a single
floor in a building, a half floor in a building, a block of buildings, or any
other physical space parameters.
Local transceivers 130a-b are mounted on printed circuit boards that fit into a
housing 132 and communicate over a backplane with a communication interface card
134 such as an E1 interface card. Any number of local transceivers can be placed
into the housing 132 to increase the number of available cells communicating
through the E1 communication interface 134. Six local transceivers per housing
is a typical configuration. Moreover, additional E1 cards can be added to boost
communication throughput. While this embodiment uses an E1 card, any
communication interface can be used with the invention such as a T1, PSTN,
Ethernet, ISDN or other type communication interface.
Two basic network configurations are anticipated: a bus configuration, where
each remote transceiver taps onto a cable; and a star configuration, where each
remote transceiver is connected via an independent cable. For example, an
in-building system can use a bus configuration where a single local transceiver
is connected to multiple remote transceivers attached to a single bus. A star
configuration, on the other hand, is configured to connect local transceivers to
multiple remote transceivers using a dedicated cable for each remote
transceiver. The actual implementation will depend on various factors including
the cell physical space parameters, the number of mobile stations that each cell
must support and the addressing technique that is used to identify the remote
transceivers and to track the mobile stations.
In the exemplary embodiment depicted in FIG. 1, the configuration is a bus
configuration and each remote transceiver 112a-c has an encoded address so that
the local transceiver 130a can identify the inbound information from the
specific remote transceiver. The mobile station communication frequencies, and
inbound and outbound TDMA time slots are assigned to the mobile station upon
call initialization and the mobile station can move among sub-sells 114a-c in
cell 115 while remaining on the same communication frequencies. Remote
transceivers 112a-c all receive the inbound information from the mobile station
and process the inbound information to determine which one has the strongest
signal. Then, the remote transceiver with the strongest signal communicates the
inbound information to the local transceiver 130a via data link 120a. Outbound
information is simultaneously transmitted by all remote transceivers 112a-c to
the mobile station on the assigned outbound frequency and during the assigned
outbound TDMA time slot.
INFORMATION PROCESSING
Inbound information is received by all of remote transceivers 112a-c and
outbound information is transmitted by all the remote receivers 112a-c. The
inbound information must be processed in an orderly fashion to assure that the
correct remote transceiver 112a-c with the strongest signal communicates the
inbound information to local transceiver 130afor each TDMA time slot. Moreover,
the outbound information must be processed in an orderly fashion to assure that
the correct power levels are transmitted according to a predefined method for
each TDMA time slot.
FIG. 2 shows the frequency allocation for the data link 120. Reference 150 is
the control information frequency between remote transceivers 112a-c and local
transceiver 130a. The control information is depicted in greater detail in FIG.
3 which shows three general divisions A, B and C. Division A is a communication
from the local transceiver to the remote transceivers. Division A has a 2 byte
preamble, a 1 byte receiver select and a 6 byte transmit power level. The
receiver select byte identifies which remote transceiver is selected to
communicate the inbound information for the following inbound information time
slot. The transmit power level 6 bytes informs the remote transceivers what
power level to transmit. Division B is a 1 byte delay allowing the RSSI
measurement. Division C is a communication from the remote transceivers to the
local transceiver. Division C has 6 bytes that communicate the RSSI levels from
the remote transceivers to the local transceiver for each of the remote
transceivers. While division C is shown to have 6 bytes, division C can be
modified to include a greater or lesser number of bytes to accommodate a greater
or lesser number of remote transceivers. The control information including
divisions A, B and C takes 576 .mu.s for a complete transfer. Each byte includes
1 start bit and 2 stop bits for 11 bits per byte of data. The result is a
minimum bit period of 3.27 .mu.s.
FIG. 2 further shows reference 152 as the inbound information frequency. This is
the frequency that the selected remote transceiver will use to communicate the
inbound information to the local transceiver for the inbound information time
slot. Reference 154 is a oscillator frequency that keeps the remote transceiver
and local transceiver synchronized. Reference 156 is the outbound information
frequency. This is the frequency that the local transceiver uses to communicate
outbound information to the remote transceivers.
A flowchart operation for the exemplary embodiment is depicted in FIG. 4. This
flowchart depicts a number of procedures that include inbound information
processing and outbound information processing. In steps 160a-c all remote
transceivers 112a-c receive inbound information from all mobile stations in the
cell and measure the received signal strength. In step 162, the selected remote
transceiver passes inbound information to local transceiver 130a and all the
remote transceivers pass RSSI information to local transceiver 130a, for each
time slot of the TDMA frame. Local transceiver 130a determines which remote
transceiver 112a-c has the greatest signal strength for each received signal.
When a mobile station moves into another sub-cell 114a-c (within the same cell
115), a stronger receive signal will be observed from a different remote
transceiver. The local transceiver will note that a new remote transceiver
should be used as the receiver, and the old remote receive should be
discontinued. The local transceiver makes a decision to transfer remote
transceivers on the next TDMA frame.
In step 164, local transceiver 130a sends outbound information to all remote
transceivers 112a-c. Along with the outbound information is power level
information depicted in FIG. 3 division A. Local transceiver 130a will vary the
power levels for each remote transceiver 112a-c every TDMA frame in order to
physically move the nulls. In step 168, the new remote transceiver is notified
of its selection for a particular received time slot for the next TDMA frame.
Step 168 then returns the process to the beginning (steps 160a-c).
The procedures described in the FIG. 4 flowchart are now described with
reference to an exemplary remote transceiver 112 and exemplary local transceiver
130.
INBOUND INFORMATION PROCESSING
FIG. 5 depicts a remote transceiver 112. A plurality of remote transceivers
112a-c are designed for deployment at various locations 114a-c to construct cell
115. Remote transceiver 112 includes a receive antenna 202 to receive an inbound
signal containing inbound information from the mobile stations. This corresponds
to flowchart step 160. Each mobile station is assigned a transmit TDMA time slot
and instructed to transmit on a particular frequency. For example, the GSM base
station receive band (corresponding to the mobile station transmit band) is from
890-915 MHz, in 200 KHz increments.
Once the inbound signal is received from the mobile station, a front end mixer
204 begins the down-conversion. Mixer 204 receives its local oscillator (LO)
input signal from filter 212, which receives its input from local transceiver
130 via an analog link over cable 120. A surface acoustic waveform (SAW) filter
208 continues the down-conversion process. The result is an inbound intermediate
frequency (IF) signal of approximately 10.7 MHz. An automatic gain control 208
serves to maintain the IF signal at a consistently high level. The IF signal is
then provided to both a switch 210 and a diversity logic circuit 214.
Switch 210 is set in the previous frame by the local transceiver 130. Switch 210
is set so that the remote transceiver with the greatest signal strength will be
selected to deliver the inbound information from the mobile station allocated to
the specified inbound time slot. That is, each remote transceiver sets its
switch 210 with respect to each time slot in the TDMA frame. For example, if a
particular remote transceiver had the greatest signal strength for mobile
stations allocated to time slots one and four, that remote transceiver would set
its switch 210 to permit the IF for time slots one and four to be transmitted
over the data link 120.
Diversity logic circuit 214 measures the inbound signal strength and generates a
received signal strength indicator (RSSI) for each inbound signal for each time
slot. This corresponds to flowchart step 162. Diversity logic circuit 214
receives a synchronization signal from synchronized timing circuits 224 in order
to properly gather the RSSI information. The RSSI information is digitized and
modulated by data modulator 216. The RSSI information is encoded into a data
word and transmitted via IF transceiver 217 to local transceiver 130 for every
reception, as shown in FIG. 3. As shown, the data word employs 16 bytes with 6
bytes (C1-C6) for communicating RSSI information from remote transceivers 112 to
local transceiver 130 via data link 120. Thus, up to six remote transceivers can
be supported in each exemplary cell. Of course, more remote transceivers can be
configured in alternate embodiments.
FIG. 6 depicts local transceiver 130 where inbound information is received over
data link 120 via IF transceiver 301 and filtered by filters 302 and 306. Filter
302 has a center frequency of approximately 10.7 MHz, while filter 306 has a
center frequency of approximately 48 MHz.
Filter 302 passes the inbound information to a GSM data detector 304 that
communicates directly with CPU 350. A signal processing function to decode the
inbound information is performed by CPU 350. Alternatively, a signal processor
can be employed to decode the inbound information. Once CPU 350 has decoded the
inbound information, CPU 350 transmits the inbound information to E1 card 134,
which transmits the information to a base station controller (BSC), mobile
services center (MSC), PBX, or other similar telephone network.
Filter 306 passes inbound RSSI information to a data detector 308. RSSI control
312 receives the RSSI information and determines which remote transceiver has
the greatest received signal strength, further corresponding to flowchart step
162. RSSI control 312 stores the RSSI information to select the inbound
information from the remote transceiver receiving the strongest signal. The
selection is performed at the next frame by sending the selection information
(FIG. 3 division A) outbound via control information data modulator 310 and
setting switch 210 in the selected remote transceiver 112. This corresponds to
flowchart step 168. This step permits RSSI control 312 to control reception from
the mobile stations on a frame by frame basis. At the next frame interval, RSSI
control 312 will instruct the remote transceiver with the strongest RSSI (from
the last frame) to operate its switch 210 to place the inbound information on
the data link 120.
OUTBOUND INFORMATION PROCESSING
Outbound information is received from a remote network via E1 card 134. CPU 350
encodes the outbound information in preparation for transmission to the mobile
stations. In this embodiment, corresponding to flowchart step 164, all remote
transceivers simultaneously broadcast the outbound information to the mobile
stations. This insures reception by the intended mobile station and reduces
control complexity. However, individual transmission by selected remote
transceivers is anticipated in an alternate embodiment.
For the outbound communication, similar to the inbound communication, each
mobile station is assigned a receive TDMA time slot and instructed to receive on
a particular frequency. For example, the GSM base station transmit band
(corresponding to the mobile station receive band) is from 935-960 MHz, in 200
KHz increments.
CPU 350 delivers the encoded outbound information to synthesizer 320 and data
modulator 322. Both these circuits communicate to a transmit exciter 324 that
passes the information to filter 326 and then to remote transceiver 112.
A problem that arises during simultaneous transmission of the outbound
information is interference. Since every remote transmitter transmits the
outbound information, overlaps will occur at various locations causing standing
nulls where no power is received by a mobile station. Standing nulls are
especially problematic in office settings where a mobile station may stay in a
single location for a period of time, such as at a desk. To alleviate the
problem of standing nulls, the outbound signal power is varied on a frame by
frame basis. This is accomplished by sending a diversity control signal to the
remote transceivers that controls the remote transceiver transmit power. This
corresponds to flowchart step 166 and is included in the control information of
FIG. 3 division A. By altering the transmit power on a frame by frame basis,
nulls are physically moved on a frame by frame basis. Thus, in operation single
frame may be lost because the mobile station is located at a null, but the next
frame will be received because the null is moved away from the previous null
where the mobile station is located. In this manner, data loss due to nulls is
practically eliminated because known error correction codes can reconstruct a
complete message with loss of information from a single frame.
Once remote transceiver 112 receives the outbound information, filter 220
receives the outbound information and passes it to power amplifier 222.
Simultaneously, data detector 218 receives the outbound information from local
transceiver 130, and passes that information to a synchronized timing circuit
224. Timing circuit 224 then adapts power control circuit 226 to vary the output
power level on a frame by frame basis as instructed by diversity control 312
(encoded in the data word). This modification of power levels serves to move
nulls and to promote high quality communication with a fixed location mobile
station.
CONCLUSION
Advantages of the present invention include improved cell boundary control,
reduced interference, fault tolerance, and more efficient use of radio
resources. Additionally, mobile users will experience improved battery life
because of lower mobile station transmit power requirements.
Having disclosed exemplary embodiments and the best mode, modifications and
variations may be made to the disclosed embodiments while remaining within the
scope of the present invention as defined by the following claims.
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