Ee-Lin Kuan

Interactive cellular and cordless video telephony: State-of-the-art system design principles and expected performance

Second-generation (2G) mobile radio standards have not been designed with video communications in mind, although the employment of error-resilient, constant-bit-rate proprietary video codecs over these systems is realistic. The third-generation (3G) systems are capable of providing higher rates and better communications integrity in support of video applications. This paper advocates the employment of burst-by-burst adaptive transceivers, which are capable of accommodating the time-variant channel quality fluctuation of wireless channels. This paper is concluded with a range of performance figures and system design guidelines for wireless systems.

Burst-by-burst adaptive joint detection CDMA

Adaptive quadrature amplitude modulation (AQAM) is combined with joint detection code division multiple access (JD-CDMA) in order to increase the throughput of a communications system, while maintaining a target BER. The QAM modes are adaptively switched, by estimating the signal to interference plus noise ratio (SINR) at the output of the joint detection receiver. For an eight-user AQAM/JD-CDMA scheme, a bits per symbol (BPS) performance of about 3.5 bits/symbol is achieved at an average SNR of about 18 dB, with a BER of approximately 0.02%, when using three different modulation modes, namely BPSK, 4-QAM and 16-QAM.

Burst-by-burst adaptive multiuser detection cdma: a framework for existing and future wireless standards

This paper provides a broad overview of the multiuser detection literature of the past few years in a nonmathematical, easily accessible approach. The treatment is then extended to the comparative study of channel-quality controlled burst-by-burst (BbB) adaptive code division multiple access (CDMA) detection such as parallel interference cancellation, successive interference cancellation, and joint detection (JD). It is demonstrated that the best complexity versus performance tradeoff is constituted by the JD receivers. Furthermore, the BbB-adaptive variable spreading factor-based schemes considered were outperformed by the adaptive quadrature amplitude modulation-based JD-CDMA schemes investigated. For example, at a channel signal-to-noise ratio per bit value of

A redundant residue number system coded burst-by-burst adaptive joint-detection based CDMA speech transceiver

E_b=N_0

Burst-by-burst adaptive joint detection CDMA/H.263 based video telephony

= 14 dB the latter scheme provides an average bit per symbol (BPS) throughput of 3.39, while the former provides an average BPS throughput of only 2.83, although the complexity of the latter is lower. In conclusion, BbB-adaptive CDMA schemes provide an attractive performance versus complexity tradeoff and are amenable to employment in both existing and future generations of wireless systems. Keywords—Adaptive CMDA systems, adaptive transceivers, interference cancellation, multiuser detection.

Burst-by-burst adaptive coded modulation-aided joint detection-based CDMA for wireless video telephony

A burst-by-burst (BbB) adaptive speech transceiver is proposed, which can drop its source coding rate and speech quality under transceiver control in order to invoke a more error resilient modem mode among less favorable channel conditions. The adaptive multirate (AMR) speech codec is operated at bit rates of 4.75 and 10.2 kb/s and combined with source sensitivity-matched redundant residue number system (RRNS) based channel codes. BbB adaptive joint detection aided code division multiple access is used for supporting the dual rate speech codec. Both the objective and subjective speech quality assessments favored the proposed BbB adaptive transceiver.

Comparative study of adaptive-rate CDMA transmission employing joint-detection and interference cancellation

Since wireless channels exhibit dramatic near-instantaneous channel-quality fluctuations, it is unrealistic to expect that a transceiver relying on time-invariant modulation and coding modes is capable of delivering as good a performance as a near-instantaneously adaptive arrangement. Hence, a near-instantaneously adaptive joint-detection code division multiple access (CDMA)-based video transceiver is proposed for wireless video telephony. Specifically, the transceiver is capable of reconfiguring itself in 1, 2 and 4 bits/symbol direct-sequence CDMA modes and delivers an unimpaired video quality associated with a peak signal-to-noise ratio (PSNR) of 34-41 dB for channel SNRs in excess of about 5 dB over the COST207 bad urban channel model at video rates between 5-26.9 kbits/s using 176/spl times/144 pixel quarter common intermediate format (QCIF) and 128/spl times/96 pixel sub-QCIF (SQCIF) video formats.

Joint-detection and interference cancellation based burst-by-burst adaptive CDMA schemes

A burst-by-burst adaptive coded modulation-aided joint detection-based CDMA (ACM-JD-CDMA) scheme is proposed for wireless video telephony and we characterise its performance when communicating over the UTRA wideband vehicular fading channels. The coded modulation schemes invoked in our fixed modulation mode based systems are trellis coded modulation (TCM), turbo TCM (TTCM), bit-interleaved coded modulation (BICM) and iterative-decoding assisted BICM (BICM-ID). When comparing the four schemes at a given complexity, TTCM was found to be the best scheme and the performance of the TTCM-assisted ACM-JD-CDMA system was evaluated using a practical modem mode switching regime.

Turbo-coded blind per-survivor processing multiuser detection CDMA

Spread adaptive quadrature amplitude modulation (AQAM) is proposed as a powerful means of exploiting the time variant channel capacity fluctuations of wireless channels and studied in comparison to the variable spreading factor (VSF) method. These two adaptive rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive code division multiple access (ACDMA) systems. More explicitly, these exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen AQAM mode or spreading factor is communicated to the remote receiver either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes with the conclusion that JD outperformed the SIC receiver in the ACDMA schemes, at the cost of increased complexity.

Joint detection based wideband burst-by-burst adaptive demodulation under co-channel interference

Spread adaptive quadrature amplitude modulated (AQAM) code-division multiple access (CDMA) is proposed as a powerful means of exploiting the time-variant channel capacity fluctuations of wireless channels. It is studied in comparison to variable spreading factor (VSF)-based techniques. These adaptive-rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive CDMA (ACDMA) systems. More explicitly, we exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen modem mode or spreading factor is communicated to the remote communicator either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes, with the conclusion that the JD outperformed the SIC receiver in the ACDMA schemes at the cost of increased complexity. Finally, the performance of the uncoded AQAM JD-CDMA scheme is also compared to that of adaptive trellis coded modulation (TCM) assisted AQAM JD-CDMA, which allows us to incorporate adaptive channel coding without any bandwidth expansion. We also show that in the particular scenario studied, adaptive TCM outperformed adaptive turbo TCM since the system was designed for maintaining a low turbo-interleaver delay.