In this paper, we show that there exists an arbitrary number of power allocation schemes that achieve capacity in systems operating in parallel channels comprised of single-input multiple-output (SIMO) Nakagami-m fading subchannels when the number of degrees of freedom L (e.g., the number of receive antennas) tends to infinity. Statistical waterfilling - i.e., waterfilling using channel statistics rather than instantaneous channel knowledge - is one such scheme. We further prove that the convergence of statistical waterfilling to the optimal power loading scheme is at least O(1/(L log L)), whereas convergence of other schemes is at worst O(1/ log L). To validate and demonstrate the practical use of our findings, we evaluate the mutual information of example SIMO parallel channels using simulations as well as new measured ultrawideband channel data.

Power Loading in Parallel Diversity Channels Based on Statistical Channel Information

In adaptive orthogonal frequency division multiplexing (OFDM)systems, different powers and rates can be allocated to subcarriers optimally by water-filling. This strategy has been proved to improve the system performance significantly. However, a large signalling overhead is induced by water-filling to contain the group of presently employed mapping schemes. The faster the channel varies in time, the more frequently the large signalling overhead is needed. In this paper, to avoid such a problem, we propose that a constant rate and different powers are allocated to subcarriers while satisfying the constraints on the transmission rate and the average bit-error rate (BER). First, an approximate relationship between BER and signal-to-noise ratio (SNR) is employed. Then, based on the convex optimization framework, the transmission power is optimally distributed to the used subcarriers with an optimal constant rate. The subcarrier assignment can be determined by an upgraded bisection method, which can be also used for other resource allocation problems. Simulations demonstrate that the proposed resource allocation strategy has better performance than water-filling with the signalling overhead considered in fast time-varying environment.

Constant-Rate Power Allocation under Constraint on Average BER in Adaptive OFDM Systems

In practice only imperfect channel state information (CSI) is available at the transmitter due to noisy and time-varying channel. In this paper, we consider optimal bit loading for orthogonal frequency division multiplexing (OFDM) with imperfect CSI subject to channel estimation. The frame length comes in as an important control parameter, while soft channel estimation and the Cramer-Rao bound are used to include the effect of channel estimation. We modify the conventional water-filling to take the maximal allowed rate on each subcarrier into account while considering CSI error. Its continuous output rates are optimally quantized by a non-iterative algorithm. Simulations show that the frame length is an important system parameter and that the computing time for the proposed algorithm linearly increases with the increasing number of subcarriers N.

/pdf/optimal-and-efficient-bit-loading-for-ofdm-in-the-presence-2h8bpixnw2.pdf

Optimal and efficient bit loading for OFDM in the presence of channel uncertainty

In wireless broadband communications, orthogonal frequency division multiplexing (OFDM) has been adopted as a promising technique to mitigate multi-path fading and provide high spectral efficiency. In addition, cooperative communication can explore spatial diversity where several users or nodes share their resources and cooperate through distributed transmission. The concatenation of the OFDM technique with relaying systems can enhance the overall performance in terms of spectral efficiency and improve robustness against the detrimental effects of fading. 

Hybrid relay selection is proposed to overcome the drawbacks of conventional forwarding schemes. However, exciting hybrid relay protocols may suffer some limitations when used for transmission over frequency-selective channels. The combination of cooperative protocols with OFDM systems has been extensively utilized in current wireless networks, and have become a promising solution for future high data rate broadband communication systems including 3D video transmission. This thesis covers two areas of high data rate networks. In the first part, several techniques using cooperative OFDM systems are presented including relay selection, space time block codes, resource allocation and adaptive bit and power allocation to introduce diversity.

Four (4) selective OFDM relaying schemes are studied over wireless networks; selective OFDM; selective OFDMA; selective block OFDM and selective unequal block OFDM. The closed-form expression of these schemes is derived. By exploiting the broadcast nature, it is demonstrated that spatial diversity can be improved. The upper bound of outage probability for the protocols is derived. 

A new strategy for hybrid relay selection is proposed to improve the system performance by removing the sub-carriers that experience deep fading. The per subcarrier basis selection is considered with respect to the predefined threshold signal-to-noise ratio. The closed-form expressions of the proposed protocol in terms of bit error probability and outage probability are derived and compared with conventional hybrid relay selection. Adaptive bit and power allocation is also discussed to improve the system performance. 

Distributed space frequency coding applied to hybrid relay selection to obtain full spatial and full data rate transmission is explored. Two strategies, single cluster and multiple clusters, are considered for the Alamouti code at the destination by using a hybrid relay protocol. The power allocation with and without sub-carrier pairing is also investigated to mitigate the effect of multipath error propagation in frequency-selective channels.

The second part of this thesis investigates the application of cooperative OFDM systems to high data rate transmission. Recently, there has been growing attention paid to 3D video transmission over broadband wireless channels. Two strategies for relay selection hybrid relay selection and first best second best are proposed to implement unequal error protection in the physical layer over error prone channels. The closed-form expressions of bit error probability and outage probability for both strategies are examined. The peak signal-to-noise ratio is presented to show the quality of reconstruction of the left and right views.

Adaptive relaying protocol multiple-input multiple-output orthogonal frequency division multiplexing systems

The performance of multicarrier systems can be enhanced by the water filling strategy, in which different rates and powers are allocated to subcarriers. However, the induced large signalling overhead leads to less transmission efficiency. To suppress this effect this article proposes an alternative strategy by dynamically assigning the same rate to each subcarrier per user. First, we quantify the asymptotic limits of its instantaneous per-symbol performance loss compared to water filling. Then, we apply this strategy to weighted sum rate maximization subject to minimum required rates and limited transmission power. Due to the simplicity of the proposed strategy, a low-complexity method is given, which can be used for other resource allocation problems in multi-carrier systems with small modifications. Simulations demonstrate that the instantaneous per-symbol performance loss of our method compared to the water filling strategy becomes insignificant if the number of users is large. The proposed method has even better performance for fast time-varying channels with respect to the signalling overhead. Moreover, given the subcarrier assignment from the proposed method, water filling can be performed and the output is close to the primal optimum.

/pdf/equal-rate-resource-allocation-for-multiuser-ofdm-2pj3b9ms1j.pdf

Equal rate resource allocation for multiuser OFDM

In this paper a simplified differential amplitude demodulation scheme is proposed for 64-DAPSK (differential amplitude and phase shift keying), which needs less quantity of decision thresholds compared with the conventional schemes. The arithmetic mean threshold (AlMT) scheme is proposed and analyzed with the simplified system in AWGN and flat Rayleigh fading channels. By these proposed schemes, system complexity is reduced considerably, but no performance degradation occurs. In the case of channel coding, the concatenated code consisting of an inner convolutional code and an outer Reed-Solomon code can be applied to 64-DAPSK. Compared with coherent 64-QAM system which employs pilot symbols for channel estimation, 64- DAPSK can achieve the performance close to or even better than that of the former by utilizing the additional redundancy for outer coding, provided that the channel SNR is high enough.

High data rate transmission with 64-DAPSK over fading channel

This paper presents a new efficient bit and power loading algorithm for orthogonal frequency division multiplexing (OFDM) systems, which aims to minimize the transmit power while maintaining a constant data rate and target bit error rate (BER). This algorithm is based on greedy allocation approach. After grouping, sorting and clustering, the greedy allocation procedure is performed over clusters other than over all subchannels. Compared with conventional optimal loading algorithms, the proposed algorithm can reduce the algorithmic complexity significantly, and the performance degradation may be negligible if algorithmic parameters are selected appropriately. Simulation results indicate advantages of the proposed algorithm

An efficient greedy loading algorithm for adaptive modulation in OFDM systems

A crucial aspect for adaptive bit and power loading algorithms is to determine all usable subchannels. In this paper, a simplified bandwidth optimization method is proposed to search for all usable subchannels for loading algorithms which aim at the minimization of power consumption with constraint of constant data rate and target bit error rate (BER). Based on this method, an efficient loading algorithm is developed. Simulation results show that the proposed algorithm can achieve the same bit allocation results to that of the well-known Hughes-Hartogs and Fischer et al. algorithm. This algorithm is appropriate for OFDM systems in time-varying channels due to its low complexity

Efficient adaptive loading algorithm with simplified bandwidth optimization method for OFDM systems

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High data rate transmission with 64-DAPSK over fading channel

An efficient greedy loading algorithm for adaptive modulation in OFDM systems

Efficient adaptive loading algorithm with simplified bandwidth optimization method for OFDM systems