This paper investigates the performance of interleave division multiple access (IDMA)-based random access with various interference canceller structures in order to support massive machine-type communications (mMTC) in the fifth generation (5G) mobile communication system. To support massive connectivity in the uplink, a grant-free and contention-based multiple access scheme is essential to reduce the control signaling overhead and transmission latency. To suppress the packet loss due to collision and to achieve multi-packet reception, non-orthogonal multiple access (NOMA) with interference cancellation at the base station receiver is essential. We use IDMA and compare various interference canceller structures such as the parallel interference canceller (PIC), successive interference canceller (SIC), and their hybrid from the viewpoints of the error rate and decoding delay time. Based on extensive computer simulations, we show that IDMA-based random access is a promising scheme for supporting mMTC and the PIC-SIC hybrid achieves a good tradeoff between the error rate and decoding delay time.

A K-user parallel concatenated code (PCC) is proposed for a Gaussian multiple-access channel with symbol synchronization, equal-power, and equal-rate users. In this code, each user employs a PCC with M+1 component codes, where the first component code is a rate-1/q repetition code and the other M component codes are the same rate-1 recursive convolutional (RC) codes. By designing the repetition coding rate and the RC component code, the K-user PCC achieve reliable transmission for a given number of users and noise level. Two decoding schemes are considered: low-density parity-check (LDPC)-like decoding and Turbo-like decoding. For each decoding scheme, a fixed point analysis is given to optimize the parameters: the rate of repetition component code 1/q, the number of RC component codes M, or the RC component codes themselves. The analysis shows that an accumulate code is the optimal RC component code for a K-user PCC, in the sense of achieving the maximum sum rate. The K-user PCC with an accumulate component code achieves a larger sum rate in the high rate region than the conventional scheme of an error correction code serially concatenated with spreading under similar encoding and decoding complexity.

Due to increasing demand for machine-to-machine (M2M) communication, simultaneous connections for many terminals are requested for current wireless communication systems. Interleave division multiple access (IDMA) has superior multiuser detection performance and attains high data transmission efficiency in multiuser communications. This paper describes the VLSI implementation of an interference canceller for OFDM-IDMA systems. The conventional architecture decreases a throughput in pipeline processing due to wait time occurring in interleave and deinterleave memory units. The proposed architecture adopts dual-frame processing to solve the problem of the wait time and achieves a high utilization ratio in pipeline stage operation. In the implementation results, the proposed architecture has reduced circuit area and power consumption by 25% and 41% for BPSK demodulation and 33% and 44% for QPSK demodulation compared with the conventional architecture on the same throughput condition.

This paper considers uplink interleave division multiple access (IDMA), of which crucial requirement is the proper operability at a very low signal-to-interference-plus-noise power ratio (SINR) range. The primary objectives of this paper are threefold: (1) to demonstrate the achievability of near-capacity performance of bit interleaved coded modulation with iterative detection (BICM-ID) using very low rate single parity check and irregular repetition (SPC-IrR) codes at a very low SINR range, and hence the technique is effective in achieving excellent performance when it is applied for IDMA, (2) to propose a very simple multiuser detection (MUD) technique for the SPC-IrR BICM-ID IDMA which does not incur heavy per-iteration computational burden, and (3) to analyze the impacts of power allocation on the convergence property of MUD as well as on the rate region, by using the extrinsic information transfer (EXIT) chart. The SPC-IrR code parameters are optimized by using the EXIT-constrained binary switching algorithm (EBSA) at a very low SINR range. Simulation results show that the proposed technique can achieve excellent near-capacity performance with the bit error rate (BER) curves exhibiting very sharp threshold, which significantly influences the convergence property of MUD. Furthermore, this paper presents results of the rate region analysis of multiple access channel (MAC) in the cases of equal and unequal power allocation, as well as of a counterpart technique. The results of the MAC rate region analysis show that our proposed technique outperforms the counterpart technique.

A K-user interleave-division multiple-access (IDMA) system with symbol-synchronous and equal-power users is considered. In this IDMA system, the spreading, interleaving, and multiple-access channel (MAC) are jointly considered as an equivalent channel, referred to as an IDMA channel. Given channel signal-to-noise ratio (SNR), the sum capacity of the IDMA channel is only determined by a K-user spread-interleave (SI) matrix. First, it is shown that to maximize the sum capacity of the IDMA channel, rows or columns of its K-user SI matrix should be pairwise orthogonal. The optimal K-user SI matrix is constructed. Second, for the IDMA system with each user employing the same spreading sequence followed by random interleaving, it is shown that, as the number of users approaches infinity, the sum capacity of the IDMA channel converges to a determinate value, which is achieved by a balanced spreading sequence. Moreover, when both the number of users and the data length approach infinity, this determinate value of sum capacity is achieved by an arbitrary spreading sequence. Furthermore, for a finite number of users, an optimal spreading sequence is derived by minimizing an expected column correlation of the K-user SI matrix. It shows that this optimal spreading sequence provides the maximum ergodic sum capacity.

The bit-error-rate (BER) performance predicted by the semi-analytical evolution technique proposed by Li Ping et al. becomes inaccurate for parallel concatenated coded interleave-division multiple-access (PCC-IDMA) systems. To solve this problem, we develop a novel evolution technique of such systems. Numerical results show that the predicted performance agrees well with the simulation results, and that this technique is useful for system optimization.

Interleave-division multiple access (IDMA) inherits the peak-to-average power ratio (PAPR) problem especially with large number of multiple layers. Clipping transmission is a really simple and efficient method, but clipping noise is a tradeoff to its performance. Due to different weighting factors, an ordering technique is considered in this letter to recursively cancel the partial clipping noise at each detection. Simulation results show that the performance is close to that of unclipped IDMA chip in the high SNR region (8-9 dB).

This paper applies iterative multiuser detection employing a new channel estimation scheme to multicarrier interleave-division multiple access (MC-IDMA), called OFDM-IDMA, which is expected to offer improved spectral efficiency in mobile communications. The MC-IDMA transmitter uses both a low-rate channel code and an individual chip interleaver for each user. The MC-IDMA receiver, which this paper focuses upon, repeats the iterative multiuser detection and soft decision-directed channel estimation (SDCE) by exploiting log-likelihood ratios (LLRs) of the coded bits which the maximum a posteriori (MAP)-based channel decoders for all users provide. SDCE estimates channel impulse responses of all users by the least-mean-square (LMS) algorithm, which aims to minimize the mean squared error between the received signal and its replica. This paper investigates the performance of MC-IDMA employing SDCE and compares it with those of three MC-CDMA techniques. Computer simulations demonstrate that MC-IDMA employing SDCE outperforms time-spread MC-CDMA and frequency-spread MC-CDMA, and that it can achieve almost the same bit error rate performance as chip-interleaved MC-CDMA while requiring lower complexity.