Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-08-21
2001-12-11
Chang, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S561000, C455S517000
Reexamination Certificate
active
06330460
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to, and finds utility within, wireless information communications systems. More particularly, the present invention relates to forward link beam forming and interference cancellation via a base station adaptive antenna array in order to increase data rate to subscriber units (mobiles) within a service sector of a wireless communication system employing e.g. a CDMA air interface.
BACKGROUND OF THE INVENTION
High-speed digital data transfers via the so-called “internet” have become ubiquitous in modern society. At the same time, the world has experienced an explosion in wireless communications technology. In well developed countries like the United States, wireless communications, particularly cellular telephone services, have proliferated as an adjunct to the wired communication network backbone. In less developed countries, wireless communication service is being developed as a primary communications medium. A need has arisen to provide digital data wireless service at ever increasing effective data rates.
Wireless radio telecommunications systems enable many mobile users or subscribers to connect to land-based wire-line telephone systems and/or digital Internet service providers enabling access to the World Wide Web digital information backbone. Conventional wireless air-interfaces include frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA), and improvements therein.
The CDMA air-interface calls for modulation of each carrier with a unique pseudorandom (pseudo-noise) code. As the CDMA users simultaneously occupy the same frequency band, the aggregate data signal transmitted by a fixed base station (forward link) is noise-like. A common pilot tone is transmitted to all mobiles within the effective service area of the base station. Individual signals are extracted at the mobile by correlation processing timed by the pilot tone.
Transfer of digital data packets differs from the transfer of digital voice information. Full duplex (simultaneous two-way) voice communication patterns imply that the data transferred between the base station and a particular mobile are real-time and substantially equal in bandwidth. It has been noted that a total delay of 200 msec (about 2 Kbit of digital data for most speech vocoders) represents intolerable latency within a voice channel. On the other hand, transfer of digital data packets is typically asymmetrical, with many more packets being sent from the base station to a particular mobile via a downlink or “forward link”, than from the mobile to the base station via an uplink or “reverse link”. In addition, for high speed data packet transfers, users appear to be far more tolerant of data transfer latencies or delays, with latencies of up to 10 seconds being encountered in current wireless data systems. While such delays appear to be tolerated by the user, the delays, attributable to relatively low effective data transfer rates, are undesirable.
One proposed solution, known as “CDMA/HDR”, uses known techniques to measure channel data transfer rate, to carry out channel control, and to mitigate and suppress channel interference. One approach of this type is more particularly described in a paper by Paul Bender, Peter Black, Matthew Grob, Robert Padovani, Nagabhushana Sindhushayana and Andrew Viterbi, entitled: “CDMA/HDR: A Bandwidth Efficient High Speed Wireless Data Service for Nomadic Users”, published on the internet at the time of filing of this application by Qualcomm Corporation at the following URL:
“http://www.qualcomm.com/hdr/pdfs/CDMA_HDR_IEEE.pdf”. The disclosure of this article is incorporated herein in its entirety by this reference thereto.
In the Qualcomm approach described in the above article, each mobile station measures the received signal-to-interference-plus-noise ratio (SINR) based on the received common pilot sent out by the base station. The data rate which can be handled by the particular mobile is proportional to its SINR. Therefore, the mobile will repetitively determine forward link SINR and communicate a maximum supportable data rate back to the base station via the mobile's reverse link channel.
Mobiles are separated into N groups or user classes according to their respective SINR levels. Time slots are assigned successively to each user class, one at a time. The average rate of transfer of data from a base station is defined as “throughput”. Latency is inversely proportional to data rate. Lower SINR (and data rate) users would ordinarily have a proportionately higher latency. However, if all users are to have essentially the same latency irrespective of individual data rate, a time slot allocation strategy inversely proportional to rate is adopted. As each user class is served, it is allocated a number of time slots inversely proportional to its rate. A compromise strategy is proposed which guarantees that the highest latency is no more than eight times the lowest individual latency, for example.
As shown in
FIG. 1
forward link packet transmissions are time-multiplexed and transmitted at a full base station power level, but with data rates and time slot durations which vary according to base-to-mobile (user) channel (forward link maximum data rate) conditions. When a mobile's data queue is empty, the base station periodically broadcasts very brief pilot and control burst information, thereby reducing interference to adjacent cells. In the proposed HDR scheme, a minimum data rate is set at 76.8 kbps using 128 byte packets and QPSK modulation, and a maximum data rate is set at 2457.6 kbps using 512 byte packets and 16QAM modulation.
While the proposed HDR method provides for a minimum data rate for each mobile, it should be apparent from inspection of
FIG. 1
that only one mobile (user) is able to receive data from the base station during a single time slot. If, for example, a first subscriber requests a data rate of 1000 kbps and a second subscriber requests a data rate of 2000 kbps, from the base station, in the proposed HDR method the service time will be divided into two service intervals, e.g. each one half second long. The first subscriber will experience a 500 kbps data rate, and the second subscriber will experience a 1000 kpbs data rate, because each subscriber is serviced not more frequently than 50 percent of the time. The average base station throughput in this example is 1500 kbps. Thus, a hitherto unsolved need has arisen for a more efficient method for sending data to a plurality of mobile stations being served by a base station.
Adaptive antenna array technologies employing feedback signals to optimize directional properties of information signals are known. Examples of spatial diversity multiple access methods employing adaptive antenna arrays are described in U.S. Pat. Nos. 5,471,647 and 5,634,199 to Gerlach et al., an article by M. C. Wells, entitled: “Increasing the capacity of GSM cellular radio using adaptive antennas”,
IEE (UK) Proc. on Comm
. Vol. 143, No. 5, October 1996, pp. 304-310; and an article by S. Anderson, B. Hagerman, H. Dam, U. Forssen, J. Karlsson, F. Kronestedt, S. Mazur and K. Molinar, entitled: Adaptive Antennas for GSM and TDMA Systems”,
IEEE Personal Communications
, June 1999, pp. 74-86.
Methods and structures for providing rapid beamforming for both uplink and downlink channels using adaptive antenna arrays are described in commonly assigned, copending U.S. patent applications Ser. Nos. 08/929,638 and 09/229,482 of co-inventor Scherzer, entitled: “Practical Space-Time Radio Method for CDMA Communication Capacity Enhancement”. Commonly assigned U.S. patent application Ser. No. 09/511,665 of co-inventors Wong and Scherzer, entitled: “Transmitting Beamforming in Smart Antenna Array Systems” describes a method for forming simultaneous forward link beams with common pilot and traffic data phase matching and without using dedicated pilots. The disclosures of the foregoing commonly-assigned patents and co-pending patent applications are incorpora
Narasimhan Ravi
Scherzer Shimon B.
Wong Piu Bill
Chang Vivian
Fulbright & Jaworski L.L.P.
Lee John J.
Metawave Communications Corporation
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