Dynamic Resource Allocation via Clustered MC-CDMA in Multi-Service Ad-Hoc Networks: Achieving Low Interference Temperature

The variation of peak-to-average power ratio (PAPR) for different allocations of spreading code sequences in multi-carrier code division multiple access (MC-CDMA) and multi-carrier direct-sequence code division multiple access (MC-DS-CDMA) systems is investigated. The results show that for a small number of active users, the PAPR performance of an MC-CDMA system can be improved by careful allocation of the spreading code sequences to different users.

Wireless networks have been evolved to heterogeneous overlay structure, in which various wireless technologies provide partial or full coverage of the service area. Another evolution direction is multi-service wireless networks. In multi-service networks, traffic of various QoS classes is serviced concurrently. In this paper, we propose a scalable and flexible network selection scheme for multi-service heterogeneous wireless networks. In the proposed scheme, the profiles are generated for users or cells to represent their characteristics in three categories, which are traffic status, mobility and QoS. The best cell is determined for each user via profile matching. The proposed scheme can be tailored to utilize the information available from the underlying wireless technologies. Via extensive simulations, it is shown that the proposed scheme handles the interplay between multi-service traffic classes more effectively than existing schemes. We discuss how the proposed scheme can be applied to the 3GPP LTE networks.

In this paper, we study secure multiple access based on multicarrier (MC) code division multiple access (CDMA) systems with induced random (chip) flipping of spreading sequence, which is suitable for machine-type communications (MTC). In MTC, devices may use low-cost hardware-based random number generators for pseudo-random noise (PN) sequences in secure communications. Since PN sequences can be estimated by correlation attacks at an eavesdropper, induced random (chip) flipping of spreading sequences is proposed to make correlation attacks infeasible. However, induced random flipping can also degrade the performance of detection and decoding at a legitimate receiver that only knows original spreading sequences. To avoid the performance degradation, we derive low-complexity iterative receiver algorithms for multiuser signal detection and decoding based on the expectation-maximization (EM) algorithm.

For future mobile communications, an appropriately chosen multiple access scheme is a critical issue. To support robust frequency planning, multi-operator scenarios, system coexistence and hierarchical cell structures, frequency division multiple access (FDMA) and multicarrier techniques are viable choices. Further multiple access schemes presently under discussion are code division multiple access (CDMA) and time division multiple access (TDMA). A mobile radio system concept deploying a hybrid frequency and time divided code division multiple access (F/T/CDMA) scheme with a multicarrier CDMA (MC-CDMA) component, called MC/JD-CDMA, is proposed and performance results for the uplink are presented. Attractive features of the proposed system concept are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, as well as inherent frequency and interferer diversity.

The multicarrier code division multiple access (MC-CDMA) system has received a considerable attention from researchers owing to its great potential in achieving high data rates transmission in wireless communications. Due to the detrimental effects of multipath fading the performance of the system degrades. Similarly, the impact of non-orthogonality of spreading codes can exist and cause interference. This paper addresses the performance of multicarrier code division multiple access system under the influence of frequency selective generalized η-µ fading channel and multiple access interference caused by other active users to the desired one. We apply Gaussian approximation technique to analyse the performance of the system. The avearge bit error rate is derived and expressed in Gauss hypergeometic functions. Maximal ratio combining diversity technique is utilized to alleviate the deleterious effect of multipath fading. We observed that the system performance improves when the parameter η increase or decreasse in format 1 or format 2 conditions respectively.

In the uplink system, different carrier frequency offsets (CFO) of different users at the receiver resulting multiuser interference (MUI) and thus degrade the performance of Multicarrier Code Division Multiple Access (MC-CDMA) system. In the previous study, Modified Minimum Mean Square Error Frequency Domain Equalization (Modified MMSE-FDE) has been proposed by Agnihotri which results in a better performance than the conventional MMSE. However, the achieved Bit Error Rate (BER) is not smaller than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> for Signal to Noise Ratio (SNR) below 20. This paper proposed a new algorithm to improve Modified MMSE-FDE performance in mitigating multiuser interference (MUI) in single cell MC-CDMA system, that is called as Carrier Frequency Offset Estimation-Minimum Mean Square Error Frequency Domain Equalization (CFO Estimation-MMSE FEQ). CFO Estimation-MMSE FEQ takes into account the rest of MUI as well as Modified MMSE-FDE to design equalization coefficient, but CFO Estimation-MMSE FEQ uses CFO estimation that is not on Modified MMSE-FDE. The value of CFO is estimated and regenerated in the receiver and then used to estimate MUI. In order to get signal processing more efficient, CFO Estimation-MMSE FEQ only takes the real trace of equalization coefficient matrix. MC-CDMA with CFO Estimation-MMSE FEQ has better performance than MC-CDMA with Modified MMSE-FDE. However, the complexity of CFO Estimation-MMSE FEQ is higher than Modified MMSE-FDE. By taking only the real trace of equalization coefficient matrix, the complexity of CFO Estimation-MMSE FEQ is getting simpler than taking the whole of equalization coefficient matrix. Furthermore, CFO Estimation-MMSE FEQ that takes only the real trace of equalization coefficient matrix is 2.9 % more efficient than CFO Estimation-MMSE FEQ that takes the whole of equalization coefficient matrix.

This paper introduces new blind time domain equalization (TEQ) techniques for downlink multicarrier code division multiple access (MC-CDMA) systems. This equalization exploits the guard interval (GI) redundancy together with the excess codes (EC) to restore the structural properties of MC-CDMA signal destroyed by multipath fading channels. Indeed, since in CDMA based wireless systems, the number of users per cell is significantly less than the spreading factor, a base station can set apart a subset of the codes, the excess codes that will not be used for spreading. It is shown that the joint use of the EC and GI redundancy improves significantly the equalization performance compared to the GI only or EC only cases. A second contribution consists in exploiting the previous information together with the one given by a pilot sequence in a semi blind scheme to further improve the performance. Finally, we propose a new adaptive algorithm for the estimation and tracking of the equalizer that has a faster convergence rate compared to existing algorithms of similar complexity order. Simulation based performance evaluations are given at the end of this paper to assess the effectiveness of the proposed methods in MC-CDMA.

This letter presents a novel multi-carrier code division multiple access (MC-CDMA) system called time domain synchronous MC-CDMA (TDS-MC-CDMA). Aided by the new training sequence (TS) with perfect autocorrelation in the time domain and flat frequency response in the frequency domain, the proposed TDS-MC-CDMA system outperform the traditional MC-CDMA system in terms of spectrum efficiency by about 10%. Simulations are carried out to demonstrate the good performance of the proposed scheme.

The performance of MMSE single‐user detection (SD) and multi‐user detection (MD) STBC multi‐carrier code division multiple access (MC‐CDMA) systems are analysed and compared in the case of two transmit antennas and one or two receive antennas over Rayleigh fading channels and then over the stochastic multiple input multiple output (MIMO) METRA channel model. With two transmit and one receive antennas, MD achieves a gain of roughly 1 dB for non‐full load systems while the same performance is obtained with MD and SD for full load systems. Besides, with two receive antennas, we present a sub‐optimal and an optimal MMSE SD MIMO MC‐CDMA schemes, this last one offering a very good performance. Finally, the very good behaviour of MMSE space‐time block coding (STBC) MC‐CDMA systems is confirmed over the realistic multi element transmit receive antennas (METRA) MIMO channel. Copyright © 2004 AEI

Multicarrier code division multiple access (MC-CDMA) is a promising technique for high data rate and high capacity (large number of users) transmission. However, rapidly time varying channels degrade the performance due to loosing the orthogonality among the subcarriers as well as code patterns. Channel estimation is very important to design adaptive system for improvement in all round performance. This paper proposes an efficient channel estimation for Rayleigh fading channel in high capacity carrier interferometry /multi-carrier code division multiple access (CI/MC-CDMA) system with variable data rate using Genetic algorithms (GAs). The system implementation is done by allocating all sub-carriers to the users who transmit high data rate and alternate odd and even subcarriers are assigned to the other sets of users transmitting at low data rate. GAs is used to estimate a near optimal solution of the set of parameter values on frequency selective Rayleigh fading channel. Objective function is formed from the weighted average of channel capacity and bit error rate. Simulation results show that both channel capacity and bit error probability are improved with the increase of number of iterations/generations.

Adaptive channel and power allocation of downlink multi-user MC-CDMA systems

Orthogonality restoring combining (ORC) performs better than maximum ratio combining (MRC) and equal gain combining (EGC) in multicarrier code division multiple access (MC-CDMA) systems under high load and high signal-to-noise-ratio (SNR) conditions. However, its exact bit error rate (BER) performance is complicated to evaluate. In this paper, the signal models for the MC-CDMA uplink and downlink channels are first unified. A lower bound and a tight approximation to the BER expressions of MC-CDMA with ORC are then developed. Both the lower bound and approximate BER expressions involve at most one-dimensional integration, hence they can be evaluated much more efficiently. The approximate BER expression is also numerically verified to be very tight under different fading conditions.

Multi-carrier code division multiple access (MC-CDMA) systems have been considered as a potential candidate for future mobile radio systems. Within this scenario, the interference originating from neighboring cells, called intercell interference, is one of the reasons for limiting the performance improvement in multicell environments. There have been many detection techniques proposed to reduce the intracell interference. Unfortunately, the mitigation of intercell interference in MC-CDMA cellular systems is still far from the desired level. This paper proposes an MMSEC-PIC receiver for MC-CDMA downlink in multicell environments. The simulation results show that the proposed scheme outperforms conventional receivers in multicell fading environments.

This paper investigates a downlink multiple-input multiple-output (MIMO) multi-carrier code division multiple access (MC-CDMA) system with iterative channel estimation (ICE) in the receiver. In MC-CDMA, each user's data symbols are spread with a Walsh-Hadamard code. Due to the superposition of different users' spread data signals, zero-valued subcarriers can occur, which cannot be used to compute least-squares (LS) estimates in ICE. For multiple transmit antennas, the data signals coincide non-orthogonal at each receive antenna. Hence, we propose two MIMO channel estimation methods to overcome these problems and avoid noise enhancement in ICE.

The performance of a multicarrier direct sequence code division multiple access (MC-DS-CDMA) system in fading environment has been extensively analysed in the literatures. The analysis that is available in the literatures did not take into account the impact of jamming and channel estimation errors on the performance of the system. In this study, closed-form expressions of the average bit error probability (BEP) of the MC-DS-CDMA system with channel estimation errors in the presence of partial band, broadband and multitone jamming are derived in a Rayleigh fading channel. The analysis shows that the magnitude of the normalised correlation between the actual and the estimated complex fading channel gain, A, greatly affects the performance of the MC-DS-CDMA system. For large signal-to-noise ratio, the average BEP with A=1 and without multiple access interference (MAI) tends to zero. When A≠1, the BEP of the system exhibits an error floor even without MAI. This error floor increases as the number of users increases. It is also shown that increasing the number of the system subcarriers enhances the system performance against jamming.