Performance of Rake receiver assisted adaptive-modulation based CDMA over frequency selective slow Rayleigh fading channels

Choi²

2007

Proc. IEEE

Section: A System Model and Aofdm Switching Levelsmentioning

confidence: 99%

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Choi²

2007

Proc. IEEE

“…This problem also constitutes a 1-D root-finding problem, rather than a multidimensional optimization problem [16]- [18]. Let us define the constraint function using (34) as (41) where we represented the set of switching levels as a vector, which is the function of , in order to emphasize that satisfies the relationships given by (35) and (36).…”

Section: Optimum Switching Levelsmentioning

confidence: 99%

“…However, the actual average BER of the adaptive scheme was not constant across the SNR range, implying that the average throughput could potentially be increased further. Hence, a per SNR optimization scheme em- ploying a modified cost function was developed to guarantee a constant target average BER across the whole operating SNR range [18]. Since Powell's multidimensional optimization may be trapped in a local optimum, rather than identifying the global optimum, the previous two schemes often result in suboptimal switching levels.…”

mentioning

confidence: 99%

Optimum mode-switching-assisted constant-power single- and multicarrier adaptive modulation

Choi

IEEE Trans. Veh. Technol.

2003

Self Cite

119

Abstract-A set of optimum mode-switching levels is derived for a generic constant-power adaptive-modulation scheme based on a closed-form expression of the average bit error ratio (BER) and the average bits-per-symbol (BPS) throughput of the adaptive-modulation scheme. This results in a constant BER, variable-throughput arrangement. The corresponding BPS throughput performance and the achievable signal-to-noise ratio (SNR) gain are investigated for the optimum mode-switching assisted constant-power adaptive-modulation schemes employing various diversity schemes, including maximal ratio combining (MRC) receive-antenna diversity, a two-dimensional RAKE receiver, as well as transmit-diversity aided space-time (ST) coding, when communicating over various fading scenarios. The BPS throughput of our constant-power adaptive quadrature amplitude modulation (AQAM) scheme approaches the throughput of variable-power variable-rate AQAM within 1 dB. However, the achievable throughput gain of the adaptive-modulation scheme, in comparison to conventional fixed-mode modems, is substantially reduced as the diversity order of the receiver is increased. Hence, adaptive modulation constitutes a lower complexity alternative to multiple-transmitter and receiver-based systems when considering the range of techniques that can be used for mitigating the effects of the channel-quality fluctuations imposed by wireless channels.Index Terms-Adaptive modulation, adaptive quadrature amplitude modulation (AQAM), fading counter measures, Lagrangian optimization for adaptive modulation, optimum switching levels for adaptive modulation.

Section: Optimum Switching Levelsmentioning

confidence: 99%

“…The authors of this contribution recently proposed a set of SNRdependent mode switching levels [25], which keeps the average BER of AQAM constant, while maximising the achievable throughput. The sets of switching levels derived in [24], [25] are based on Powell's multidimensional optimisation technique [26] and hence the optimisation process may become trapped in a local minimum. In order to overcome this problem, we derived an optimum set of switching levels [27] employing the Lagrangian multiplier technique and showed that this set of switching levels results in the global optimum in a sense that the corresponding AQAM scheme obtains the maximum possible average BPS throughput, while maintaining the target average BER.…”

Section: Optimum Switching Levelsmentioning

confidence: 99%

RAKE receiver detection of adaptive modulation aided CDMA over frequency selective channels

Choi

IEEE 54th Vehicular Technology Conference. VTC Fall 2001. Proceedings (Cat. No.01CH37211)

Self Cite

Abstract-A closed form Bit Error Ratio (BER) formula is derived for a fixed-mode Quadrature Amplitude Modulation (QAM) scheme employing Rake receivers and receiver antenna diversity. The analysis is extended to constant power Adaptive QAM (AQAM) expressing the average BER and the average throughput as a closed form function of the modulation mode switching levels. Then, the switching levels are optimised so that the average throughput is maximised, while maintaining a given target BER. This results in a constant-BER, variable-throughput arrangement. The results show that our constant-power AQAM scheme exhibits an SNR gain of about 5dB in comparison to fixed-mode QAM, when operating over a Wireless Asynchronous Transfer Mode (W-ATM) channel employing one antenna. However, the achievable throughput gain of the system over conventional fixed-mode modems is substantially reduced, as the diversity order of the receiver is increased.