In this paper, we present a new codebook design motivated by statistical properties of multiple-input multiple-output (MIMO) channels generated by 3GPP TR 38.901, a specification document targeted for 5G new radio (NR). The beamforming vectors of the proposed codebook are chosen from discrete Fourier transform (DFT) beams to cover a variable range of angular channel distributions, while maintaining the double codebook structure composed of long-term and short-term beam groups. Effectiveness of the codevector selection is visualized in a multi-dimensional index space where the search result as well as standard codevectors are indicated for comparison. The proposed codebook is shown to exhibit a significant performance gain over different carrier frequency ranges and channel types.

As the number of antenna elements increases in multiple‐input multiple‐output (MIMO) systems, an efficient feedback and beamforming strategy becomes more important to achieve the desired bandwidth efficiency required by the next‐generation wireless systems. The authors investigate the statistical characteristics of the MIMO channel generated by the three‐dimensional spatial channel model to recognise some of the limitations inherent in the existing codebooks adopted by the current third generation partnership project specifications. Such limitations include unnecessary co‐phasing combinations for cross‐polarised (X‐pol) antenna arrays and, in particular, long‐term codevector selections, which are not best suited to the channel distributions. In this study, the observed shortcomings are improved by proposing a new multi‐rank codebook applicable to the X‐pol array of antenna elements supporting up to the quadruple rank. The proposed beamforming codevectors are presented using variable parameters so that they can be adapted to changing channel characteristics. The efficiency of the proposed codebook is further improved by eliminating redundant co‐phasing values. The performance of the proposed codebook is evaluated using the TR 36.873 urban macro environment and its effectiveness is demonstrated by quantifying its gain over the existing codebooks.

In this paper, we propose channel training and beamforming schemes to maximize the benefit of large-scale antenna, or massive multiple-input multiple-output (MIMO) systems. The proposed schemes are operated by transmitting continuous precoding matrix indicator (PMI) feedback signals through a series of pattern. Conventional communication systems, such as LTE systems, use PMI, rank indicator (RI), and channel quality indicator (CQI) to report the channel state information (CSI) to the enhanced node B (eNB), with an increasing feedback overhead as the number of antenna elements increases. The proposed beamforming and feedback schemes solve this problem by iterative CSI reports and codebook extension. Each PMI report is conducted based on a component codebook of smaller size, and cumulated feedback information is utilized to build an extended beamformer. The proposed methods are applicable to many different types of wireless systems, including frequency division duplex (FDD) systems which do not possess the channel reciprocity assumed by many of earlier works. The methods also ensure the backward compatibility which allows the operation of legacy user equipment (UE). The continuous feedback process also enables the enhancement of the codebook resolution. The resulting system performance improvement is verified by computer simulation results.

In this paper, we propose strategies to mitigate inter-cell interference by using remote radio heads (RRHs) installed at cell edge areas. For conventional systems, all user equipments (UEs) located in the coverage of a macro base station (BS) are assumed to be scheduling candidates for the corresponding cell. This makes UEs located near cell edge areas experience significant inter-cell interference. The proposed strategies solve the problem by virtually extending the coverage area to be larger than the area where the scheduling candidates are located. The advantage of the coverage extension is mainly obtained from a concept of moving cell boundaries, which is realized by partially activating the RRHs in a time-division fashion. Based on the Monte-Carlo simulations, performance benefits of moving boundary schemes over the static boundary schemes are presented.

In this paper, we propose a codebook construction method for multiple-input multiple-output (MIMO) beamforming systems operating under the per-antenna power constraint (PAPC). Under the PAPC which limits the individual power of each transmit antenna, it is known that only phase steering information is required to form the optimal beamforming vector at the transmitter. For systems with non-reciprocal uplink and downlink channels, the optimal phase steering information should be chosen at the receiver based on the estimated channel state information, and fed back to the transmitter through rate-limited feedback links. To efficiently encode the phase steering information in the feedback messages, phase steering codebooks have been previously proposed in the literature. In order to exploit the temporal correlation property of the wireless fading channels, we propose to use the phase tracking information between adjacent feedback slots as feedback messages, and provide the construction algorithm for the phase tracking codebook. The objective function for the phase steering codebook is reformulated as a new objective function for the phase tracking codebook to apply the generalized Lloyd-Max vector quantization (VQ) algorithm. The performance of the two codebooks is evaluated and the effectiveness of the proposed codebook is demonstrated by Monte-Carlo simulations.

We consider distributed multiple-input multiple-output systems with remote antennas (RA) connected to the base station via high-capacity backhaul, which are operated under the per-antenna power constraint (PAPC). We propose a simple strategy to determine the transmission power for each user, referred to as channel norm-based power control (NBPC) to obtain near-optimal performance in terms of the sum-rate maximization and the log-sum-rate maximization for fairness improvement, applicable to any number of RAs and users. In particular, a closed-form solution to maximize the sum-rate using the NBPC is presented. We also show that the proposed strategy used in conjunction with existing multi-user transmission schemes derived under the total power constraint can be efficiently applied to systems under the PAPC.

Wireless systems equipped with distributed antennas can provide enhanced data throughput as well as improved signal quality when appropriate cooperative transmission schemes among antennas are employed. In this paper, the performance of distributed antenna systems (DAS) under the influence of Rayleigh fading and log-normal shadowing effects is investigated for different cooperation strategies, and corresponding statistical distributions for both the signal-to-interference ratio (SIR) and the capacity are presented. Specifically, the ergodic capacity per remote antenna (RA) is determined when n RAs cooperatively transmit the desired signal to the target receiver, which is compared with the non-cooperative single-antenna transmission (SAT) case. Using the results, a preferable mode of operation for given geographic locations of the receiver is determined. We further propose to perform an adaptive operation between the cooperative and non-cooperative modes under the capacity maximization criteria, and quantify exact amounts of capacity gain over individual transmission modes.

Although spatial multiplexing (SM) is an efficient means to enhance the data throughput in multiple-input multiple-output (MIMO) systems, its performance becomes seriously degraded when the receiver carrier-to-interference ratio (CIR) becomes low. In such a situation, which is typical for mobile terminals located near the boundaries of cells with low frequency reuse, transmission schemes with reduced spatial rate including space-time coding (STC) and the cyclic delay diversity (CDD) exhibit improved performance. In this paper, we consider rate-1 downlink transmission for MIMO systems with multi-antenna terminals in use, and focus on the analysis of the receiver performance at the low CIR region (cell boundary). Instead of using the conventional signal detection scheme under the 2-Tx and 2-Rx channel model, we show the effective CIR increases when the spatial demultiplexing (SD) detection is performed under the 4-Tx and 2-Rx model considering the strongest interfering signal as well as the desired signal. Through the evaluation of the effective CIR, the performance improvement at the cell boundary by using this "intercell SD (ISD)" which can cancel out or mitigate the strongest interference is demonstrated. It is shown the proposed scheme has the effective CIR gain of 3.04 dB at the cell boundary location.

Closed-form expressions for the ergodic capacity for downlink transmission of a distributed antenna system are derived, based on different cooperative transmission schemes including single-antenna transmission (SAT) and dual-antenna transmissions (DAT). For DAT, we consider space-time block coding (STBC) for the open-loop operation, and maximum ratio transmission (MRT) for the closed-loop operation. The probability density function (PDF) of the signal-to-interference ratio (SIR) for each scheme is presented, followed by the capacity expressions in terms of the received power components for the significant signal sources and the interference sources. The switching criteria among the transmission schemes are proposed and used for evaluating the capacity gain over the conventional SAT. The derived results are verified via Monte-Carlo simulations in a Rayleigh fading environment, for a given geographic location of the mobile station (MS). It is also demonstrated that an instantaneous adaptation of the transmission schemes, if applicable, can provide further capacity improvement over individual transmission schemes.

The covering polynomial method is a generalization of error-trapping decoding and is a simple and effective way to decode cyclic codes. For cyclic codes of rate R0, equal to n/spl rho/+2V/spl radic/n/spl rho/+(1/2) log/sub /spl phi//(n//spl rho/)+O(1), where /spl phi/=(1+/spl radic/5)/2. For all codes correcting up to three errors, the number of covering polynomials is at least n/spl rho/+2/spl radic/n/spl rho/+O(log n); covering polynomial sets achieving this bound (and thus within O(log n) of the minimum) are presented in closed-form specifications for rates in the range 11/15/spl les/R<3/4.

We propose a channel classification method that identifies the delay path profile of Rayleigh fading channels, which can be used in conjunction with conventional maximum-likelihood sequence estimation (MLSE) receivers. The proposed method determines the appropriate number of delay taps for the MLSE trellis, based on a decision variable obtained from multiple traffic bursts. By formulating the decision variable using the F-distribution, we derive exact expressions for misclassification probability. A new MLSE receiver structure that utilizes the channel classification method is described, and bit error rate (BER) simulation results are presented to demonstrate the performance improvement. The particular application which is discussed is the IS-136 TDMA standard.

In this paper, the performances of burst detection schemes which employ constant false-alarm rate (CFAR) algorithms are analyzed and compared. These schemes can be used for a typical time division multiple access (TDMA) protocol. The burst detection probabilities and corresponding false-alarm probabilities are derived to understand the effect of the received signal quality degradation at the receiver for any constant modulus signals. The burst detection probabilities are expressed as a function of the received signal quality measure which can be expressed as a function of cross-ambiguity function. Two particular detection schemes, namely, the single window ratio detection (SWRD) scheme and the double window ratio detection (DWRD) scheme, are compared in terms of the robustness against the degradation of the received signal quality.

A demodulation receiver structure that gives desirable performance for fading channels with and without delay spread is proposed. Using a decision variable derived from the channel response estimate, the new scheme identifies the delay spread of the channel and performs either maximum-likelihood sequence estimation (MLSE) or symbol-based detection operation to demodulate the received signal. Particular application discussed is the IS-136 North American TDMA cellular standard operating at cellular and PCS frequency bands. Simulation results show that the BER performance of the combined receiver structure is virtually identical to the symbol-based detection performance for the flat fading channel and the MLSE performance for the two-ray fading channel.