Bit loading with BER-constraint for multicarrier systems

Abstract

Abstract-We present discrete adaptive bit loading algorithms for multicarrier systems with uniform (nonadaptive) power allocation operating in a frequency selective fading environment. The algorithms try to maximize the overall throughput of the system while guaranteeing that the mean bit error rate (BER) remains below a prescribed threshold. We also study the impact of imperfect subcarrier signal-to-noise ratio information on throughput performance. Results show that the proposed algorithms have approximately the same throughput and mean BER as the optimal allocation while having a significantly lower computational complexity relative to other algorithms with near-optimal allocations. Moreover, when compared with algorithms that employ approximations to water filling, the computational complexity is comparable while the overall throughput is closer to the optimum.

Mean BER minimization loading algorithm for linear precoded OFDM

“…BER is obtained from SER using the approximation [3]. Using this approximation, the optimization problem can be given as…”

“…Classically, to achieve a target error rate, SER is fixed on each subcarrier which is equal to the global SER of an OFDM symbol, since all the constellation sizes of QAM have the same value of the SNR gap at the same SER, as it is clear from (2). In this approach, an approximate relation between SER and bit error rate (BER) is used [2] to achieve the target BER of the system, which results in the violation of the target BER in some cases as discussed in [3]. One solution is to fix the BER rather than SER on each subcarrier as proposed in [4].…”

“…Here, we will consider another approach, where rather than fixing the BER at each subcarrier, target BER of a complete OFDM symbol will be achieved, hereafter known as mean BER. This approach has been discussed in [3] and [5].…”

Bit and Power Loading for OFDM-Based Three-Node Relaying Communications

“…This can be realized by minimizing the Lagrangian (14) where is the transmit-power on the th subcarrier, and the Lagrangian multiplier for the constraint . It can be shown that is a convex and increasing function of .…”

“…The rate-adaptive approach is to maximize the number of bits per block subject to the fixed transmit-power and the target link performance. This approach has also received considerable applications in the OFDM systems (e.g., [14]). …”