Multi-carrier Code Division Multiplexing Research Articles

Intelligent and secure transceiver design and implementation for future wireless communication

In this work, we have proposed an intelligent and secure transceiver design and implemented over RF testbed for future wireless communication. To secure the communication, first of all, physical layer security (PLS) has been proposed for underlay multiple-input multiple-output cognitive radio network (MIMO-CRN) by using a bi-directional zero-forcing beamforming. Secondly, (PLS) has been proposed by using transmit beamforming for non-orthogonal multiple access (NOMA) over multiple cells and in the presence of primary user and secondary users. The proposed model has been extended for MIMO-NOMA over double cell and multiple scenarios. To improve further security an adaptive transceiver has been designed where parameter can be varied as per the system requirement and meantime, an intelligent received is developed in which parameter can be estimated through a blind process. The modulation format is also classified for single carrier, orthogonal frequency division multiplexing (OFDM) and MIMO through a statistical method. Finally, sequence design has been proposed to improve peak average power ratio for OFDM and multicarrier code division multiplexing (MC-CDMA). These sequences can also remove multiuse user interference for CDMA system over asynchronous system by improving the correlation properties within a code.

Joint Transmitter–Receiver Frequency-Domain Equalization in Generalized Multicarrier Code-Division Multiplexing Systems

Joint transmitter-receiver optimization in generalized multicarrier code-division multiplexing (GMC-CDM) systems is investigated in this paper. The optimization consists of a one-tap post-frequency-domain equalizer (post-FDE) and a one-tap pre-FDE. While the one-tap post-FDE is optimized under the criterion of minimum mean square error (MMSE), the one-tap pre-FDE is achieved through three stages of optimization, which are operated at different levels and motivated to achieve, possibly, different objectives, including maximum throughput and maximum reliability. Specifically, in our three-stage pre-FDE, the first-stage pre-FDE is operated at the symbol level, concerning only the symbols within a group. The second-stage pre-FDE is carried out at the group level for harmonization among the groups. Finally, the third-stage pre-FDE handles group partition. In this paper, the error and throughput performance of the GMC-CDM systems is investigated when assuming communications over frequency-selective Rayleigh fading channels. It can be shown that the reliability or throughput of the GMC-CDM systems can be significantly improved by employment of the proposed pre- and post-FDE schemes. Furthermore, the pre- and post-FDE algorithms obtained can be implemented with high flexibility, which facilitates a GMC-CDM system to achieve a good tradeoff between its throughput and reliability.

An Efficient Low-Complexity Detector for Spatially Multiplexed MC-CDM

We propose a novel suboptimum detection method for spatially multiplexed multicarrier code division multiplexing (SM-MC-CDM) communications. Compared to the spatially multiplexed OFDM (SM-OFDM), the frequency domain spreading in SM-MC-CDM systems results in an additional diversity gain. To take advantage of diversity and multiplexing while mitigating interference, we design a low complexity efficient detector called unified successive interference cancellation (SIC) detector for SM-MC-CDM communications. Further performance improvement is achieved by adopting in conjunction with the unified SIC the iterative subcarrier reconstruction-detection algorithm originally proposed for single antenna systems. The results demonstrate significant performance improvement over other existing methods of comparable complexity. A close approximation for the probability density function (pdf) of the proposed detector's output signal-to-interference plus noise ratio (SINR) is found and used to obtain error bounds for the bit error rate (BER). Performance of the coded SM-MC-CDM transmission is also discussed in the paper.

Performance of MC-CDM Systems With MMSEC Over Rayleigh Fading Channels

In this paper, we investigate the performance of multicarrier code-division multiplexing (MC-CDM) systems with minimum mean square error combining (MMSEC) over a Rayleigh fading channel. An approximated expression on the symbol error rate (SER) for MMSEC is derived. The approximated expression provides an accurate approximation of the true SER, particularly for systems with higher modulation and a small spreading factor. Through the derived error performances, we also calculate the achievable diversity order. MC-CDM systems with MMSEC achieve the same asymptotical diversity order of 1, regardless of the spreading factor. Within practical signal-to-noise ratio (SNR) ranges, the effective diversity order is further increased as a larger spreading factor is used. The derived analytical expressions are verified by numerical and simulation results.

Turbo equalization with cancelation of nonlinear distortion for CP-assisted and zero-padded MC-CDM schemes

In this paper, we consider MC-CDM schemes (MultiCarrier Code Division Multiplexing) where clipping techniques are employed to reduce the envelope fluctuations of the transmitted signals. Both CP-assisted (Cyclic Prefix) and ZP (Zero- Padded) MC-CDM schemes are studied. We develop frequencydomain turbo equalizers combined with an iterative estimation and cancelation of nonlinear distortion effects, with relatively low complexity since they allow FFT-based (Fast Fourier Transform), frequency-domain implementations. Our performance results show that the proposed receivers allow significant performance improvements at low and moderate SNR (Signal-to-Noise Ratio), even when strongly nonlinear transmitters are employed. The receiver for ZP MC-CDM is of special interest for systems where the duration of the channel impulse response is not a small fraction of the duration of the MC-CDM blocks, being suitable to MC-CDM systems with very large blocks (hundreds or even thousands of subcarriers), since they do not require the inversion nor the multiplication of large matrixes.

Performance of spatially multiplexed MC-CDM with zero-forcing unified successive interference cancellation detection

Spatially multiplexed multicarrier code-division multiplexing (SM-MC-CDM) is a multiple-input multiple-output, orthogonal frequency division multiplexing (MIMO-OFDM) communication technique with multiple antennas used for spatial multiplexing and with frequency domain spreading on each antenna. Unified successive interference canceller (U-SIC) is an efficient detector recently introduced for SM-MC-CDM. This paper presents an analytical approach to the performance of zero-forcing (ZF) U-SIC for SM-MC-CDM communications. For a system with an equal number of transmit and receive antennas, an approximation for the probability density function of post-detection signal-to-noise ratio (SNR) is used to derive a closed-form analytical upper bound and approximations for the probability of error and ergodic capacity. It is shown that SM-MC-CDM with ZF U-SIC is able to achieve higher diversity order than that achieved by ZF and minimum mean squared error (MMSE) V-BLAST detectors used on each subcarrier of a MIMO-OFDM system with the same number of subcarriers. The diversity order obtained increases with the number of subcarriers. It is also shown that the ergodic capacity of the system decreases with increasing number of subcarriers.

BER analysis of group-orthogonal multicarrier code-division multiplex systems

Group-orthogonal multi-carrier code division multiple access (GO-MC-CDMA) has recently been proposed as a promising technique for the uplink segment of wireless systems. In this paper we propose and analyze a related scheme, group-orthogonal multi-carrier code division multiplexing (GO-MC-CDM), suitable for the downlink segment of the future generation of wireless systems. The proposed system is shown to offer a similar bit error rate (BER) performance as the downlink version of GO-MC-CDMA at a fraction of its computational complexity. An analytical expression for the BER when using maximum likelihood (ML) detection is derived providing valuable insight into the parameters affecting the system performance and providing a basis for its optimization. Simulation results using parameters and (correlated) channel models aiming at the next generation of wireless systems are provided confirming the analytically derived results.

A Multicarrier Multiplexing Method for Very Wide Bandwidth Transmission

The multicarrier orthogonal code division multiplexing (MC-OCDM) introduced here has been designed for very wide bandwidth (VWB) point-to-point and point-to-multipoint transmission. In order to meet VWB transmission requirements, the MC-OCDM design has two components, the basic and the composite. The basic MC-OCDM is a generalized form of the standard orthogonal frequency division multiplexing (OFDM). It has the property of distributing the power of each transmitted symbol into all subcarrier frequencies. Each subcarrier will then carry all transmitted symbols which are distinguished by orthogonal Hadamard sequences. The resulting system is shown to improve the performance of OFDM by introducing frequency and time diversity. As shown, by both analysis and simulation, the basic MC-OCDM combats the effects of narrowband interference (NBI). In particular, the simulation results show that the BER performance of the basic MC-OCDM in the presence of NBI is better than OFDM for both coded and uncoded systems. Furthermore, the composite MC-OCDM is a method of orthogonal frequency division multiplexing (OFDM) basic MC-OCDM channels. This allows us to multiplex more than one basic MC-OCDM channel into a VWB transmission system which can have the performance and spectral efficiency required in fixed wireless transmission environments.

Multicarrier Access and Routing for Wireless Networking

A multicarrier access and routing system has been proposed for use in wireless networks. Users within each cell access a radio port (RP). All RPs are connected to a radio exchange node (REN) which routes the calls or packets. The uplink access is orthogonal multicarrier code-division multiple access (MC-CDMA) and the downlink transmission is multicarrier orthogonal code-division multiplexing (MC-OCDM). The REN contains a switch module which provides continuous routes between wireless terminals without demodulation/remodulation or channel decoding/reencoding. The switch module is nonblocking and has complexity and speed linearly proportional to its size. Also, the switch module does not introduce interference into the network. Any existing interference or noise in its input port is transferred to its output port. The input-output switch connections are assigned on demand by a control unit. A random input/output port assignment process can achieve maximum switch throughput.

A Frequency Scheduling Method for MC-CDM

Multi-carrier code division multiplexing (MC-CDM) is one of promising multiplexing techniques for fourth-generation mobile downlink communications systems, where high data rate services should be provided even for high speed-cruising mobiles. For MC-CDM-based packet communication, a frequency scheduling method, which adaptively assigns different sub-carriers to different users, is proposed. This paper proposes a frequency scheduling method, which utilizes pre-assignmented subcarriers in the frequency domain for the MC-CDM scheme. Furthermore, the performance of the proposed system in frequency selective fading channels is compared with that of a no-scheduled MC-CDM scheme by computer simulation in both single- and multi-cell environments. From the results, it is found that the proposed system achieves better bit error rate performance than the no-scheduled MC-CDM scheme and can control quality of service (QoS) for active users.

Spread Spectrum‐Based Subcarrier Recovery Method for Multi‐Carrier Code Division Multiplexing System

AbstractA time domain Spread Spectrum (SS)‐based subcarrier recovery method is proposed for down‐link Multi‐Carrier Code Division Multiplexing (MC‐CDM) system, which periodically inserts SS pilot signals into data signal stream in a time division manner at the transmitter. Instantaneous channel impulse response is first estimated by correlating the received pilot signal at the receiver, and then corresponding instantaneous frequency response essential for subcarrier recovery is calculated from the Discrete Fourier Transform (DFT) of the estimated impulse response. The SS pilot‐assisted method is also applicable to Direct Sequence (DS)‐CDM system as a means to estimate instantaneous channel impulse response for Rake combining, and taking the same approach in both MC‐CDM and DS‐CDM systems, there is no large difference between them in terms of transmission efficiency and receiver complexity. The proposed MC‐CDM system must be a promising down‐link multiplexing protocol, because it can achieve better bit error rate (BER) performance than the DS‐CDM system with the same SS pilot‐assisted Rake combiner in frequency selective fast Rayleigh fading channel.