TD-SCDMA中码道激活算法研究

介绍了TD-SCDMA物理层中有关扩频部分的技术,并针对不同的高层配置,即在不同时隙不同码道的配置下,着重分析上行和下行码道激活的基本原理以及关键技术。

A FINE GRANULAR JOINT SOURCE CHANNEL CODING METHOD

An improved FGS (Fine Granular Scalability) coding method is proposed in this letter, which is based on human visual characteristics. This method adjusts FGS coding frame rate according to the evaluation of video sequences so as to improve the coding efficiency and subject perceived quality of reconstructed images. Finally, a fine granular joint source channel coding is proposed based on the source coding method, which not only utilizes the network resources efficiently, but guarantees the reliable transmission of video information.

LDPC based time-frequency double differential space-time coding for multi-antenna OFDM systems

Differential space-time coding was proposed recently in the literature for multi-antenna systems, where neither the transmitter nor the receiver knows the fading coefficients. Among existing schemes, double differential space-time (DDST) coding is of special interest because it is applicable to continuous fast time-varying channels. However, it is less effective in fre- quency-selective fading channels. This paper’s authors derived a novel time-frequency double differential space-time (TF-DDST) coding scheme for multi-antenna orthogonal frequency division multiplexing (OFDM) systems in a time-varying fre- quency-selective fading environment, where double differential space-time coding is introduced into both time domain and fre- quency domain. Our proposed TF-DDST-OFDM system has a low-complexity non-coherent decoding scheme and is robust for time- and frequency-selective Rayleigh fading. In this paper, we also propose the use of state-of-the-art low-density parity-check (LDPC) code in serial concatenation with our TF-DDST scheme as a channel code. Simulations revealed that the LDPC based TF-DDST OFDM system has low decoding complexity and relatively better performance.

Hierarchical Code Assignment Algorithm and StateBased CDMA Protocol for UWSN

The characteristics of underwater acoustic channel such as long propagation delay and low bit rate cause the MAC(Medium Access Control) protocols designed for radio channels to be either inapplicable,or have low efficiency for UWSN(Underwater Sensor Network).We propose a hierarchical and distributed code assignment algorithm based on divisive probability function which can avoid conflict between spread codes with high probability,and provide a statebased MAC protocol for UWSN.Without RTS/CTS(Request To Send/Clear To Send) handshaking,each node maintains a neighbor table including state field,and packages are forwarded according to the state of the receiver,so it can avoid the interference caused by transmitting to a sending node in a half-duplex system and improve channel utilization.The design of power control minimizes the nearfar effect inherent in CDMA.Simulation results reveal that state-based CDMA protocol shows outstanding performance in throughput,delivery ratio and resource-consumption.

Differential space-time modulation in rapidly fading channels

Previously proposed differential modulation schemes for time-varying channels may not achieve the full transmit diversity and the maximum Doppler diversity simultaneously. Based on an existing basis expansion model, a new differential space-time code, which wisely combines interleaver/de-interleaver with traditonal space-time transmitting technique to overcome such limitation, .is presented. Two noncoherent differential decoders, named decision-feedback differential detector （DF-DD） and Viterbi-algorithmbased multiple-symbol-detection differential detector （ MSD-DD）, are also derived. We show that our design may recover data symbols with full antenna diversity and the maximum Doppler diversity at high signal-to-noise ratio. System performance is evaluated with simulations.

CHANNEL ESTIMATION OF MULTI-RATE DS-CDMA SIGNALS IN SLOW FADING MULTIPATH CHANNELS

In Direct-Sequence Code Division Multiple Access(DS-CDMA) mobile communi-cation systems, it is very important to obtain accurate estimation of the channel parameters,especially that of the propagation delay. But the near-far problem may make the estimationcomplicated and can degrade the estimation performance significantly. In this paper, an efficientMaximum Likelihood (ML) method is presented for channel parameter estimation of multi-rateDS-CDMA systems in slow fading multipath channels in a near-far scenario. The algorithmextended the ML approach to multi-rate DS-CDMA systems, and proposes decomposing a multi-dimensional optimization problem into a series of one-dimensional optimization and has improvedcomputational efficiency. Theoretical analysis and numerical examples show that the estimatorproposed is effective and near-far resistant.

Video coding bit allocation algorithm over wireless transmission channel

For two-way video communications over wireless channels using the automatic repeat request (ARQ) retransmission scheme, TMN8 rate control scheme is not effective in minimizing the number of frames skipped and cannot guarantee video quality during the retransmissions of error packets. This paper presents a joint source channel bit allocation scheme that allocates target bits according to encoder buffer fullness and estimation of channel condition by retransmission information. The results obtained from implementing our scheme in H.263+coder over wireless channel model show that our proposed scheme encodes the video sequences with lower and steadier buffer delay, fewer frames skipped and higher average PSNR compared to TMN8.