16QAM与8PSK 软解调算法

Samuelsam

【文件名】:06630@52RD_01258317.rar
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【简　介】:Abstract—In this paper, we present a log-likelihood ratio (LLR)
based approach to analyze the bit error rate (BER) performance
of quadrature amplitude modulation (QAM) on Rayleigh fading
channels without and with transmit diversity. We derive LLRs
for the individual bits forming a QAM symbol both on flat fading
channels without diversity as well as on channels with transmit
diversity using two transmit antennas (Alamouti’s scheme) and
multiple receive antennas. Using the LLRs of the individual bits
forming the QAM symbol, we derive expressions for the probability
of error for various bits in the QAM symbol, and hence the
average BER. In addition to being used in the BER analysis, the
LLRs derived can be used as soft inputs to decoders for various
coded QAM schemes including turbo coded QAM with transmit
diversity, as in high speed downlink packet access (HSDPA) in
3G.
Keywords – QAM, BER analysis, transmit diversity, log-likelihood ratio.
【目　录】:
I. INTRODUCTION
II. LLR AND BER IN FLAT FADING
III. LLR AND BER IN TRANSMIT DIVERSITY
IV. CONCLUSIONS

Samuelsam

【文件名】:06630@52RD_00814830.rar
【格　式】:rar
【大　小】:235K
【简　介】:Abstract—Recently, turbo codes have received great attention
due to their outstanding performance. Unfortunately, a high
performance is associated with large transmission delays, prohibiting
an application for speech transmission. Hence, the aim
of this paper is the comparison of turbo codes employing short
interleavers with convolutional codes in terms of bit error rate
performance and computational effort. Additionally, a pragmatic
approach of bandwidth-efficient turbo-coded modulation is considered.
Analyzing the structure of transmitter and receiver,
interesting results are presented concerning the design of the
mapper. Furthermore, a new very simple soft-output demodulation
algorithm is derived. In order to compare turbo codes with
convolutional codes under realistic conditions, both are embedded
in a direct sequence (DS) code division multiple access system.
Besides this comparison, a compromise between a high coding
gain (low code rate) and high direct-sequence spreading is worked
out, including the consideration of the turbo-coded modulation
scheme. Simulation results indicate that turbo codes with small
block interleavers do not outperform conventional convolutional
codes. Furthermore, it is shown that for coherent demodulation,
low code rates and low DS spreading is superior to high code
rates and high DS spreading.
Index Terms—Code division multiple access (CDMA), turbo
coded modulation, turbo codes.
【目　录】:
I. INTRODUCTION
II. TURBO CODES
III. TURBO-CODED MODULATION
IV. CDMA SIMULATION MODEL
V. SIMULATION RESULTS
VI. CONCLUSION

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