This paper presents a simple yet effective method for designing nested families of LDPC codes. Rate compatible codes are essential for many communication applications, e.g. hybrid automatic repeat request (HARQ) systems, and their design is nontrivial due to the difficulty of simultaneously guaranteeing the quality of several related codes. Puncturing can be used to generate rate-compatible LDPC codes, but it produces a gap to capacity that, in practice, often significantly exceeds the gap of the mother code. We propose an alternative method based on successively extending a high-rate protograph. The resulting codes not only inherit the advantages of protograph codes, namely low encoding complexity and efficient decoding algorithms, but also cover a wide range of rates and have very good performance with iterative decoding thresholds that are within 0.2 dB of their capacity limits.

/pdf/the-design-of-rate-compatible-protograph-ldpc-codes-2vn32p7d4i.pdf

The Design of Rate-Compatible Protograph LDPC Codes

This paper presents a simple yet powerful method for designing embedded rate-compatible families of LDPC codes. Rate compatible codes are essential for many communication applications, e.g. hybrid automatic repeat request (HARQ) systems, and their design is nontrivial due to the difficulty of simultaneously guaranteeing the quality of several related codes. Puncturing can be used to generate rate-compatible LDPC codes, but it produces a gap to capacity that, in practice, often significantly exceeds the gap of the mother code. We propose an alternative method based on successively extending a high-rate protograph. The resulting codes not only inherit the advantages of protograph codes, namely low encoding complexity and efficient decoding algorithms, but also cover a wide range of rates and have very good performance with thresholds that are all within 0.15 dB of their capacity limits.

/pdf/the-design-of-rate-compatible-protograph-ldpc-codes-3jbqdje4zg.pdf

The design of rate-compatible protograph LDPC codes

Zadoff-Chu (ZC) sequences have been used as synchronization sequences in modern wireless communication systems, replacing the conventional pseudorandom noise sequences due to their perfect autocorrelation properties. We first study the problem of ambiguity between a timing offset and a frequency offset, which arises when a ZC sequence is used as a synchronization signal. We then show how a frequency offset can impair the timing property of a ZC sequence, causing irreducible timing errors. An analytical framework, particularly the timing spectrum, is developed, which fully characterizes a ZC sequence's timing properties and its fundamental limitations as a time synchronization sequence in the presence of a frequency offset between the transmitter and the receiver. This analytical framework provides a powerful analytical tool for timing signal design and performance analysis of ZC sequences.

Analysis of the Frequency Offset Effect on Zadoff–Chu Sequence Timing Performance

The arrival of the 5G NR provides a unique opportunity for introducing new inter-cell interference coordination (ICIC) mechanisms. The objective is twofold: to better exploit the benefits of ICIC in coherence with the rest of radio resource management (RRM) principles in 5G, and to support new services and deployment scenarios. We propose several enhanced techniques. In the uplink, inter-cell coordination of the pilot sequence configuration mitigates the inter-cell interference problem of such pilots, which is especially severe for cell-edge users. In the downlink, coordinated small cell DTX aims at network interference control and energy consumption reduction, whereas intercell rank coordination can unleash the potential of advanced receivers with minimal control overhead. Besides, on-demand power boosting and coordinated muting can be tailored to meet URLLC requirements. The simulation results quantify the performance benefits of the different techniques under heterogeneous key performance indicators (KPIs). We also discuss the standardization effort required for having each of these techniques included in the 5G NR specifications.

/pdf/interference-coordination-for-5g-new-radio-4juze8qxnt.pdf

Interference Coordination for 5G New Radio

An apparatus and method for encoding a channel in a communication system using a Low-Density Parity-Check (LDPC) code. The method includes determining a number of parity bits to be subjected to puncturing; dividing the parity bits at predetermined intervals, and determining a number of puncturing bits, which are subjected to puncturing within the predetermined intervals; determining positions of puncturing parity bits corresponding to the determined number of puncturing bits; and repeatedly performing puncturing on the puncturing parity bits corresponding to the determined positions at the predetermined intervals. The predetermined intervals are determined by dividing a length of parity bits by a length of one column group in a parity-check matrix.

Method and apparatus for channel encoding and decoding in a communication system using low-density parity-check codes

In this paper, we propose an efficient puncturing method for LDPC codes. The proposed algorithm provides the order of variable nodes for puncturing based on the proposed cost function. The proposed cost function tries to maximize the minimum reliability among those provided from all check nodes. Also, it tries to allocate survived check nodes evenly to all punctured variable nodes. Furthermore, the proposed algorithm prevents the formation of a stopping set from the punctured variable nodes even when the amount of puncturing is quite large. Simulation results show that the proposed punctured LDPC codes perform better than existing punctured LDPC codes.

Efficient Puncturing Method for Rate-Compatible Low-Density Parity-Check Codes

In this paper, optimal pilot sequence designs for MIMO-OFDM systems in multi-cell environments are provided. The proposed multi-cell optimality criterion is to minimize the worst-case MSE of an LS-based channel estimator. To satisfy the multi-cell optimality, it is found that the pilot sequence set, having the perfect auto-correlation property, should meet the Welch bound and the maximum magnitude of the cross-correlation function should be further minimized. Multi-cell optimal pilot sequence designs for various pilot types and their DFT representations are proposed by adopting Chu sequences and a tight upper-bound on the maximum size of the pilot sequence set is derived for a given pilot sequence length and the maximum allowed cross-correlation value. Simulation results show that the proposed pilot sequences can improve both the MSE performance and the system performance in multi-cell environments.

Optimal Pilot Sequence Design for Multi-Cell MIMO-OFDM Systems

In this paper, we analyze the cross-correlation properties for Chu sequences, which provide information on the distribution of the maximum magnitudes of the cross-correlation function. Furthermore, we can obtain the number of available sequences for a given maximum magnitude of the cross-correlation function and the sequence length.

pdf/generalized-cross-correlation-properties-of-chu-sequences-332os622v3.pdf

Generalized Cross-correlation Properties of Chu Sequences

In this paper, the channel estimation and pilot sequence design technique of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in multi-cell environments are studied for situations in which the inter cell interference (ICI) is the dominant channel impairment. We design pilot sequence aiming at minimizing mean square error and propose the channel estimation technique correspond to the designed pilot sequences. The proposed pilot sequences employ the sequences with good correlation properties such as Chu sequence and through simulations, it is shown that channel estimation algorithm using designed pilot sequence is effective for mitigating the ICI.

http://www.koreascience.or.kr:80/article/JAKO200909659870079.pdf

Optimal Pilot Sequence Design based on Chu sequences for Multi-cell Environments

In this paper, the SSs for cell search are designed in multi-cell systems. The proposed SSs minimize the maximum magnitude of the cross-correlation function for a given length and the maximum number of supportable cells within a group is obtained for a given SS length and the maximum allowed cross-correlation value among the sequences. The simulation results show that the proposed signals have a distinct advantage in multi-cell environments.

Synchronization signal design for cell search in 3GPP-LTE HCN

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