A latency reduced method is proposed based on the modified successive cancellation (MSC) decoder for decoding polar codes. In the MSC decoder, it was shown that latencies for both the rate-zero and the rate-one nodes can be reduced. By redistributing the information bits, the proposed method can obtain a good rate-zero and rate-one nodes distribution, in which decoding latency can be further reduced under the MSC decoder. Simulation results show that the new polar code (obtained by the proposed method) achieves 8.5% latency reduction with neglected error performance loss compared with the original polar code. Furthermore, it is easy to adjust the trade-off between the error performance and decoding latency by the proposed method.Introduction: Recently, polar codes [1] have attracted a great deal of interest since they are the first codes to provably achieve channel capacity with low-complexity encoding and decoding algorithms in a diverse set of scenarios. Although theoretically very interesting, polar codes have some drawbacks practically. Because of the nature of sequential decoding, the traditional successive cancellation (SC) decoders suffer from a very high latency. In [2], it has been shown that the latency of a rate-one node (introduced later on) can also be reduced like a rate-zero node, in which significant latency reduction is achieved with no sacrifice in error performance. For a polar code with fixed block length, the rate-one and rate-zero nodes distribution is determined by the information set. In this Letter, we propose a method to give a minor adjustment to the original information set and to obtain a new information set with good rate-zero and rate-one nodes distribution, in which decoding latency can be further reduced with small performance loss compared with the original information set.

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In this paper, the impact of path loss exponents on antenna location design in generalized distributed antenna system (GDAS) is investigated, with the goal of maximizing a lower bound of the average uplink capacity. A simple case when antenna ports (AP) are uniformly placed along a circle is studied first. Both the upper and lower bounds for the optimal placement radius are given. An approximate expression of the optimal radius with sufficient accuracy is derived using Newton-Cotes integration formula with a degree of 5. The given expression indicates that with different path loss exponents the optimal locations of APs differ. The interesting thing is that the optimal radius decreases as the path loss exponent grows when the number of APs is large, while it is the opposite when the number of APs is small. Analytical results are then extended to more general scenarios and a new criterion is proposed for antenna location design. Simulation results show that the given criterion outperforms those in previous literature, and the achieved capacity gain can be as much as 10%.

Bit error rate (BER) performance of the OFDM system has been widely studied on multi-path fading channel with the channel gain being modeled as various distributions. But the statistical distribution of the OFDM signal on the receiver side has neither been well studied, nor given the closeformed expression. In order to design the optimum detection criteria, especially for the hypothesis test of the OFDM symbol, the probability density function (pdf) of the received OFDM signal on the multi-path channel is presented in this paper. At first, the pdf of the frequency domain impulse response of the channel is derived through the characteristic function method. Secondly, we can show that the joint pdf of the complex channel frequency response and the complex additive white Gaussian noise leads to the pdf of the received OFDM symbol under the condition of given transmitted symbol on a given subcarrier. Lastly, the theoretical analysis is verified by the simulations, and the theoretical and simulation results agree with each other perfectly.

In this paper, the outage performance of multiuser multiple-input single-output (MISO) systems exploiting joint spatial and multiuser diversities is investigated for Rayleigh fading channels with outdated feedback. First, we derive closed-form exact outage probabilities for the joint diversity schemes that combine user scheduling with different spatial diversity techniques, including: 1) transmit maximum-ratio combining (TMRC); 2) transmit antenna selection (TAS); and 3) orthogonal space-time block coding (OSTBC). Then the asymptotic outage probabilities are analyzed to gain more insights into the effect of feedback delay. It is observed that with outdated feedback, the asymptotic diversity order of the multiuser OSTBC (M-OSTBC) scheme is equal to the number of transmit antennas at the base station, while that of the multiuser TMRC (M-TMRC) and the multiuser TAS (M-TAS) schemes reduce to one. Further by comparing the asymptotic outage probabilities, it is found that the M-TMRC scheme outperforms the M-TAS scheme, and the M-OSTBC scheme can perform best in the outage regime of practical interest when the feedback delay is large. Theoretical analysis is verified by simulation results.