DS/CDMA reverse link structure for high data rate transmission

Details DS/CDMA reverse link structure for high data rate transmission DS/CDMA reverse link structure for high data rate transmission

2000-12-07

2004-05-11

Pham, Chi (Department: 2667)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S478000

Reexamination Certificate

active

06735185

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to Direct Sequence (DS) Code Division Multiple Access (CDMA) communications systems and more particularly to a code structure and method for increasing data transmission speed in the reverse channel.
BACKGROUND OF THE INVENTION
Mobile wireless communication technology has gained such widespread acceptance that mobile communication devices, which includes mobile phone handsets, pagers, and wireless communicators (integrated digital voice and data communications) are rivaling their land-based counterparts in popularity for use for not only voice communication, but also for data transmission, such as facsimiles, Internet access, electronic mail, messaging, and video transmission. In any wireless communication system, a key goal is to obtain the greatest data throughput for an allocated frequency. However, in each mobile communication technology, the frequency allocations are limited, raising the potential for exceeding a system's capacity with too many users and uses. Digital technologies, which include TDMA (time division multiple access), digital FDMA (frequency division multiple access), and code division multiple access (CDMA) provide increased subscriber capacity of the allocated bandwidths as well as to provide higher quality signals for transmission. In digital communications systems, clarity and throughput of the transmitted information is controlled by the amount of data that can be transmitted over a given channel within the allocated spectrum. For every increase in the data rate, there is a corresponding increase in the quality of the call, i.e., the voice clarity, and/or the amount of other data that can be transmitted, which may be control information for the transmission itself or data to be communicated from one site to another.
The reverse link, or reverse channel, is the one-way communication from the mobile unit to a base station. Information on the reverse channel consists of primary traffic (voice or data), secondary traffic (data), and signaling using frames of having lengths, in IS-95-based systems, of 20 ms each. Conventional reverse links transmit a stream of digitally-encoded RF packets which consist of digitally-encoded voice (or data) packets interspersed with digitally-encoded power adjustment commands. The use of a packet configuration for data transmission, along with the unique coding, permits a single frequency channel to be simultaneously used for transmission of many different signals. According to the Telecommunications Industry Association/Electronic Industries Association (TIA/EIA) IS-95 standard, “Mobile Station-Base Station Compatibility Standard for Dual-mode Wideband Spread Spectrum Cellular Systems”, IS-95-based CDMA systems may transmit data for a single call reverse link at one or four different rates: 9600 bits per second (bps), 4800 bps, 2400 bps, or 1200 bps for rate set 1. In the IS-95 standard, a frame is defined as a 20 ms burst of digitally-encoded data consisting of sixteen equal length power control groups (PCG). Each power control group consists of six 64-ary Walsh codes. Since a 64-ary Walsh code carries six bits of baseband data, the conventional Walsh coded IS-95 frame may carry 6×6×16 bits, for a total of 576 baseband bits or code symbols. The 576 coded bits are convolutionally decoded by a rate_decoder to obtain 192 bits per frame (at 9600 bps.) Of these 192 bits, 172 bits are information bits, which presents a significant limiting factor for reverse channel data rates under the current standards. (The remaining bits comprise twelve frame quality bits and eight encoder tail bits.)
Methods have been proposed for increasing the number of data bits that can be transmitted during a given time period. One such method is described in U.S. Pat. No. 5,465,269 of Schaffner, et al., in which a supplementary signal is provided using differential coherent modulation of the in-phase (I) and quadrature phase (Q) signals by 180□. (The disclosure of this patent is incorporated herein by reference.) This method provides as many as 96 additional data bits, and therefore, is well suited for transmitting relatively simple control information such as power control commands. However, this 50% increase in the number of data bits is not sufficient to accommodate the demands for data rates of several times the current data rate capabilities.
FIG. 1
provides a block diagram of a basic prior art core process sequence for generating and modulating one reverse CDMA channel. The quality/CRC (cyclic redundancy check) indicator
102
, convolutional encoder
103
for error detection and correction, repeater
104
, which maintains a constant input to block interleaver
105
. Interleaver
105
ensures that sequential data is randomly distributed to combat the effects of Rayleigh fading. The data stream is then fed through modulator and spreading block
101
. Walsh modulator
106
outputs one Walsh function for every six input symbols. Data burst randomizer
107
provides variable rate transmission capability. At modulo-2 adder
108
, the long code mask from long code generator
109
is used to direct-sequence (DS) spread the signal output by modulator
106
. The DS spread signal is split to modulo-2 adders
110
and
111
where it is spread in quadrature with the I (in phase) and Q (quadrature) PN sequences. The Q channel has a half-chip delay
112
added to create an offset (OQPSK), and the I and Q channels are filtered by baseband filters
113
and
114
, respectively, to limit the signals to the appropriate transmission bandwidth. The I and Q channels are modulated by the I and Q carrier signals at mixers
115
and
116
, respectively, combined together at adder
117
, and sent to the antenna (not shown.)
As is known, the reverse CDMA channel consists of 2
42
−1 logical channels, with one logical channel permanently and uniquely associated with each mobile station, thus providing means for addressing and identifying multiple mobile stations over a common CDMA channel. This addressing is accomplished through manipulation of the long code, which is a period 2
42
−1 LFSR (linear feedback shift register) sequence, that is used for spreading the reverse link. There is only one long code sequence, with different mobile stations being distinguished by the relative phase of the long code. The long code mask is a 42-bit number which is used to select specific bits from the long code. It is this long code mask that serves as the reverse link address. Under the IS-95 standard, when transmitting on an access channel, a mobile station constructs the 42-bit long code mask from a fixed nine bit sequence (“110001111”) (bits M
41
through M
33
), the access channel number (ACN: bits M
32
through M
28
), the paging channel number (PCN: bits M
27
through M
25
), the base station identity (BASE_ID: bits M
24
through M
9
), and the pilot PN (pseudorandom noise) offset for the forward CDMA channel (PILOT_PN: bits M
8
through M
0
). (See, e.g., IS-95, Section 6.1.3.1.8-2). When transmitting on a reverse traffic channel, the mobile station uses a long code mask constructed from its electronic serial number (ESN (permuted): bits M
31
through M
0
), along with a fixed ten bit sequence (“1100011000”) (bits M
41
through M
32
). Under IS-95, this latter code is designated the “Public Long Code Mask”. The ESN of a mobile station cannot be readily altered, thus providing a level of privacy protection for the mobile user. The IS-95 standard also provides for an alternate private identification number (private long code) which may be used in place of the ESN. Under the current standards, the initial ten bit sequence is not varied in any way, thus providing a stable code, currently not allocated for any other purpose.
SUMMARY OF THE INVENTION
It is an advantage of the present invention to utilize existing code structures within the IS-95 standard to provide a significant increase in the data rate of transmitted signals.
It is another advantage of the present invention to provide the abili

Affiliated with

Also associated with

Rating

DS/CDMA reverse link structure for high data rate transmission does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with DS/CDMA reverse link structure for high data rate transmission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DS/CDMA reverse link structure for high data rate transmission will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3241630