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This letter analyzes the performance of uplink integrated sensing and communications (ISAC) systems where communication users (CUs) and radar targets (RTs) share the same frequency band. A non-orthogonal multiple access (NOMA) protocol is adopted in the communication procedure of the ISAC system. Novel expressions are derived to characterize the outage probability, ergodic communication rate, and sensing rate. Besides, the diversity order and high signal-to-noise ratio (SNR) slope are unveiled to gain further insights. It is found that when achieving the same communication rate, the ISAC system enjoys a higher sensing rate than the conventional frequency-division sensing and communications (FDSAC) system where CUs and RTs share isolated bands. All the results are validated by numerical simulations and are in excellent agreement., 5 pages

Beamspace multiple-input multiple-output (MIMO) systems leverage the lens antenna array to reduce their hardware cost, which is a promising technology in millimeter wave (mmWave) frequency bands. This letter proposes a novel signal-to-leakage-plus-noise ratio (SLNR)-based beamspace precoding and beam selection scheme to improve the downlink sum rate (SR) of the beamspace mmWave massive MIMO channels. First, for a given beam subset, a SLNR maximization-based beamspace precoder is designed to mitigate the inter-user interference caused by leakage power, thus enhancing the SR. Then, an approximated expression of the SR is formulated, based on which an iterative radio frequency (RF) precoding and beam selection method is designed to further improve the system SR. Numerical results demonstrate a superior SR performance of the proposed scheme over state-of-the-art methods.

Beam selection can alleviate the requirement on the number of radio frequency (RF) chains in lens array-assisted millimeter Wave (mmWave) multiple-input multiple-output (MIMO) systems. This letter investigates the performance of joint user and beam selection in a multi-user discrete lens arrays (DLA) communication system. To reap the maximum throughput, we jointly optimize the beam selection and user selection. Specifically, two algorithms are formulated based on stable matching and greedy search in order to find a proper subset of users and beams. Simulation results show that the proposed methods can achieve almost the same performance as the exhaustive-search-based method but involve much lower complexity.

To evaluate the performance of wireless multi-path channels with discrete inputs, this letter investigates the ergodic mutual information (EMI) of a generalized fading type named mixture gamma distribution (MGD) under $M$ -ary quadrature amplitude modulation ( $M$ -QAM) signaling. An accurate closed-form expression for the EMI is developed to approximate the exact value. The MGD fading can be specialized into several regularly used fading cases including Rayleigh fading, Nakagami- $m$ fading, $\eta -\mu $ fading, $\kappa -\mu $ fading, and ${\mathcal {K}}_{G}$ fading, and then the corresponding closed-form EMI formulas are separately derived to measure these fadings. Compared with the Gaussian source signals based research on MGD fading, this work sheds light on the performance with discrete inputs instead of Gaussian inputs, thereby being more practical. This study can be regarded as a unified tool to evaluate the EMI with discrete inputs over arbitrary wireless channels.

This letter proposes a novel joint decoding scheme for correlated sources using systematic polar codes. In the proposed scheme, each source independently encodes its message into a systematic polar code word and sends the codeword via a binary-input additive white Gaussian noise channel to the common destination, where adaptive cyclic redundancy check-aided successive cancellation list (CA-SCL) decoders are employed. During the iterative decoding process, the log likelihood ratios (LLRs) fed to each adaptive CA-SCL decoder are iteratively combined with the extrinsic LLRs from other decoders. The correlation among the sources is exploited to improve the decoding performance. Simulation results show that, in comparison with independent decoding, the proposed scheme can achieve significantly improved decoding performance without increased complexity.

In this letter, we develop a recurrence formula for the capacity of Nakagami- $m$ fading channel with BPSK/QPSK modulations when channel state information is available at the receiver. For each fading parameter $m$ , a simply constructed series representation with a fast-convergence rate can be obtained through the recurrence formula. The series expansion provides a numerically efficient way to calculate the capacity for both Rayleigh and Nakagami- $m$ fading channels. The simulation results show that the recurrence formula is a good alternative for estimating the capacity of Nakagami fading channel.

This letter proposes an efficient approach to evaluate the word error rate (WER) of channel codes with the distribution of squared radius of decision regions. The squared radius can be measured via simulations and then the WER for any signal to noise ratio (SNR) can be evaluated. In addition, by approximating the distribution of squared radius as Gamma distribution, only the mean and variance of squared radius need to be measured. For long codes, the WER can be further simplified to a single term of incomplete gamma function or Gaussian Q function. Moreover, for the code family which has a threshold SNR, the squared radius can be used to estimate the threshold SNR.

This letter studies the information-theoretic sum capacity of the reverse link for multi-cell, multi-user cellular systems subjected to a peak power constraint. It is proven that, for the optimal scheduling, there will be at most one user transmitting at part of the peak power within each cell. Therefore, we approximate the optimization scheduling problem to a combination optimization problem which can be solved by standard simulated annealing algorithm. Further, we propose a low complexity cell greedy scheduling algorithm which can achieve almost the same performance as simulated annealing algorithm.

In the literature, the marginal probability density function (pdf) of the smallest eigenvalue of Wishart matrix has been known in the form of determinants having elements with special functions. In this letter, a polynomial expression is derived on the pdf of the smallest eigenvalue of complex central Wishart matrix with correlation at the side with the smallest number of antennas.

In this letter, a new method for decoding turbo-like codes is proposed to simplify the hardware implementation of Log-MAP algorithm. In our method, the multivariable Jacobian logarithm in Log-MAP algorithm is actually concatenated by recursive 1D Jacobian logarithm units. Two new approximations of Log-MAP algorithm based on these 1D units are then presented, which have good approximated accuracy and is simple for hardware implementation. We further suggest a novel decoding scheme that its complexity is near the Max-Log-MAP while the performance is close to the Log-MAP algorithm.