Researches On Capacity-approaching Detection/de-coding Algorithms And Error Control Technologies

Communication networks have greatly facilitated people's daily life,work,study and entertainment.They also plays an important role in the social public services and the transformation of government functions.On the other hand,the requirement for high-quality lowcost communications in the growing consumer market promote the research work in constant progress.From a technical point of view,the way to improve the network performance is to study the the capacity-approaching transmission technologies and high-efficient communication protocols.This thesis conducts the research work from the transmission point of view, including the physical layer,cross-layer,link layer and network layer.And it obtains some detection/decoding algorithms and error control technologies as follows:First,it studies the detection of partial response signals and proposes a new type of lowcomplexity iterative detection algorithm for coded signals under intersymbol interference.1) the BCJR based decision feedback detector(BCJR-DFD) is used for the detection of continuous phase modulation(CPM) signals and the performance is obtained under the neglection of error propagation assumption.2) the BCJR-DFD based iterative detection/decoding algorithm for partial response coded signals is proposed,whose performance is evaluated via simulation.This algorithm is also analyzed by EXIT Chart and the SNR threshold is obtained. 3) the new iterative algorithm is used for both the detection of LDPC-CPM coded signals and the RSCC coding schemes,then the performance evaluations are done via simulation.Let A and B be the complexity of the detector and decoder,respectively.Then the total amount of computing for traditional iterative algorithm is N_iter(A + B) after the N_iter-th iteration,while it's only A + N_iterB for the new iterative algorithm,which significantly reduces the complexity. At the same time,simulation results also show that the new algorithm approaches closer to the ideal performance.Second,it studies the cross-layer codec based on the irregular LDPC,both the crosslayer iterative decoder(CLID) and nest LDPC codec scheme are proposed using the unequal error protection(UEP) of irregular LDPC.According to the CLID,the link layer CRC detects the corrected decoded frames and modifies its prior information,then it's used for helping to correct other bits in the next iteration.The elite frame with much lower frame error rate (FER) has much higher probability to be used for helping to correct other bits.CLID can effectively approach the Shannon limit without adding additional redundancy.Based on a similar principle,in the link layer of nest LDPC codec,a very high rate LDPC(inner code) is nested to the elite bits of the irregular LDPC which servers as the outer code in the physical layer.The further protection by inner code makes the elite bits have much higher probability to be used for helping to correct other bits in the outer code.The nest LDPC effectively reduces the distance from Shannon limit at the expense of adding only a small amount of additional redundancy.This thesis also proves the performance gain and analyzes the iterative decoder numerically.Third,it studies the anti-jamming error control issue for the data-transmission in frequencyhopping communications,and proposes a type-ⅡHARQ scheme based on the half-rate invertible linear block codes for the reliable transmission of small data burst.1)Training sequences is used for the detection of human interference and the bad-frame is discarded.2)The invertibility of half-rate BCH codes is extended to the universal linear block codes and is used for reducing the computational complexity in the receiver.3)The double-error correction multiple-error detection CRC decoder is designed to improve the throughput under high SNR.4)Equal gain combining is used in order to take advantage of the past transmissions to reduce the probability of retransmission and thus to improve the throughput under low SNR. The performance is analyzed theoretically,both the exact results for all SNR and the approximate expression for moderate to high SNR is obtained.At the same time,the performance obtained by the key technology is also analyzed theoretically.Simulations under different channels are carried for both the BCH and LDPC based schemes,the results show that the new scheme in the special application has a very high throughput.Finally,it studies the loss recovery issue in the packet-switched networks and a ratecompatible algebraic(RCA) Erasure Codes is proposed for the loss recovery in broadcasting small files.RCA codes can be constructed incrementally by recursive method,so it shows a high degree of rate-compatibility in the receiver.This makes the RCA based loss recovery schemes can adapt the time-varying channel.After describing the definition and codec algorithms of RCA codes,the end-to-end loss recovery scheme based on RCA codes is proposed. And the performance is evaluated via simulation.The results show that the RCA-based loss recovery scheme working in the network with loss rate(?)∈[0,1/2) can achieve near capacity performance when it is used for small file broadcasting.