Handset diversity in wireless communications system

Details Handset diversity in wireless communications system Handset diversity in wireless communications system

2000-10-24

2004-09-28

Gary, Erika (Department: 2681)

Telecommunications

Receiver or analog modulated signal frequency converter

With wave collector

C455S101000, C455S222000, C455S223000, C455S224000, C455S225000, C455S226100, C455S272000, C455S272000, C455S278100, C455S500000, C455S063400, C320S118000, C342S452000

Reexamination Certificate

active

06799026

ABSTRACT:

BACKGROUND
1. Field of Invention
The present invention relates to, and finds utility within, wireless information communications systems. More particularly, the present invention relates to diversity reception of downlink signals at the handset without requiring dual receive chains.
2. Related Art
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.
The CDMA air-interface is in a state of constant improvement. A latest iteration of the CDMA standard is known as “third generation” or “3G”. For digital data traffic one proposed solution for CDMA 3G is known as “CDMA/HDR”, or simply “HDR”. 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.qua1comm.com/hdr/pdfs/CDMA_HDR_IEEE.pdf”. The disclosure of this article is incorporated herein in its entirety by this reference thereto. Principles articulated in this paper are being incorporated into a draft 3G specification, known as “Draft Baseline Text for the Physical Layer Portion of the 1×EV Specification” being proposed within the Third Generation Partnership Project Two (3GPP2), the disclosure thereof being incorporated herein in its entirety by this reference thereto.
In the 1×EV approach described in the above draft specification, 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.
FIG. 1
graphs the 1×EV forward link (base station to mobile unit) traffic channel, as well as reverse link data rate control channel and acknowledgement channel along a common time base. In accordance with the 1×EV specification, forward link traffic channel and reverse link control channel physical layer packets can be transmitted in 1 to 16 time slots, with each time slot being 1.66 milliseconds in duration at a data rate of 153.6 kbps. When more than one time slot is allocated to a subscriber, the forward link transmit slots use a 4-slot interlace. That is, adjacent transmit slots of a particular 4096 bit traffic packet are separated by three intervening slots, and slots of other packets are transmitted in the slots between those transmitted slots. If a positive acknowledgement is received on the reverse link ACK channel that the physical layer packet has been received on the forward link traffic channel before all of the allocated slots have been transmitted, the remaining untransmitted slots will not be transmitted and the next allocated slot is used for the first slot of the next physical layer packet transmission.
Diversity reception is a recognized technique to reduce effects of signal fading and/or co-channel interference. In this method, a resultant signal is obtained by a combination or selection, or both, of two or more sources of received-signal energy that carry the same modulation or user information content (“traffic”), but may differ in signal strength, or signal to interference plus noise (SINR), at any given instant. For example, a base station may transmit the same traffic simultaneously via two separate frequencies. Two receive chains of a mobile unit then provide the required two sources of received-signal energy for combinatorial diversity reception with each chain tuned to a respective one of the frequencies.
Open loop diversity is proposed for CDMA 3G air-interfaces, for example “orthogonal transmission diversity” or “OTD”. In the OTD approach, the base station includes two transmit channels for transmitting simultaneously two coded signals via two spatially separated antennas. Each channel is coded with a unique Walsh code so that its information content or “traffic” is orthogonally related to the other channel's otherwise identical traffic. The mobile station or handset simultaneously receives the two signals at its antenna, amplitude and phase matches one of the received signals to the other via a RAKE receiver, and decodes the two Walsh coded channels, thereby enabling the information content of the channels to be combined in proper amplitude and phase in order to reduce effects of fading and co-channel interference. A block diagram depicting a base station BTS
10
having two transmit channels
12
and
14
is set forth in FIG.
2
. Channel
12
includes an antenna or antenna array
16
, and channel
14
includes an antenna or antenna array
18
. Antennas
16
and
18
are, e.g., spatially separated. Antenna
16
transmits a signal over path
20
and antenna
18
transmits a signal over path
22
.
Signal paths
20
and
22
arrive at an antenna
24
of a handset
26
. Signal path
20
includes the forward link traffic and first interference, for example, and signal path
22
includes the same forward link traffic (coded to be orthogonal with respect to the traffic on path
20
) and second interference. A RAKE receiver within handset
26
separates the two channels by virtue of the orthogonality of the Walsh coding, amplitude matches and phase matches the two channels, and combines the two channels together in a manner providing diversity reception.
As illustrated by
FIG. 2
, the OTD approach requires providing more transmit channels at the base station
10
. If the base station
10
includes an antenna array for beam forming in order to provide coherent spatial gain at the mobile station or handset, implementing the OTD method requires two antenna arrays, thereby doubling the number of transmit channels, or reducing potential coherent gain by about 3 dB. One potential drawback of the OTD method is that each subscriber unit, e.g. handset
26
, being serviced within the particular service sector requires two Walsh codes. While the OTD method proposes using QPSK modulation in order to double the number of available Walsh codes, there are ultimately only a finite number of available Walsh codes. Therefore, a base station potentially becomes capacity-limited to one half of the number of subscribers that can be simultaneously served with an air-interface using only a single Walsh code per subscriber unit, given the same finite number of available Walsh codes. Another drawback found with the OTD method is that if two channels and antennas are used to transmit from the base station, for much of the time the two channels will remain highly correlated at the handset location, and the advantages otherwise provided by diversity reception will not be realized.
One example of a receiver architecture for concurrent diversity reception is provided by U.S. Pat. No. 6,014,570 to co-inventor Piu Bill Wong and Donald Cox, e

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