In this paper, we present a frame synchronization method which consists of the non-orthogonal superposition of a synchronization sequence and the data. We derive the optimum detection criterion and compare it to the classical sequential concatenation of synchronization and data sequences. Computer simulations confirm the benefits of the non-orthogonal allocation for the case of short frames, which makes this technique particularly suited for the increasingly important regime of low latency and ultra- reliable communication.

This paper presents an overview of the coding aspects of a GNSS receiver. Coding allows detection and correction of channel-induced errors at the receiver, here the focus is on the mitigation of threats from malicious interferences. Although the effects of interference at different stages of GNSS baseband processing has been deeply analyzed in the literature, little attention was devoted to its impact on the navigation message decoding stage. Theis paper provides an introduction to the various coding schemes employed by current GNSS signals, discussing their performance in the presence of noise in terms of block-error rate. Additionally, the benefits of soft-decoding schemes for navigation message decoding are highlighted when jamming interferences are present. The proposed scheme requires estimating the noise plus interference power, yielding to enhanced decoding performances under severe jamming conditions. Finally, cryptographic schemes as a means of providing anti-spoofing for geosecurity location-based services, and their potential vulnerability are discussed, with particular emphasis on the dependence on the dependence of the scheme on successful navigation message decoding.

In this paper we develop two new approaches for frame synchronization in the binary-input AWGN channel, in which we account for the sign ambiguity of the received symbols and exploit knowledge of an alternating sequence which precedes the synchronization word. We present an approach based on an extended sliding window and the appropriate decision metric. For the common case that the synchronization word is followed by encoded data we present a solution which exploits the error detection capability of the channel decoder and applies a list decoding approach for frame synchronization. The proposed methods are validated through computer simulations in the deep-space communication uplink and show significant performance gains compared to current solutions.

We consider Incremental Redundancy Hybrid Automatic Repeat reQuest (IR-HARQ) in which the code rate and modulation of the initial transmission and all retransmissions are adjusted based on average channel statistics. In the absence of instantaneous channel state information at the transmitter (CSIT), we present a method which computes, prior to transmission, the optimum code rates and modulations and explicitly considers a given maximum number of retransmissions. For the case that additional feedback on CSI of previous transmission attempts is available, we present two heuristic schemes which exploit this knowledge and offer increased throughput at the cost of higher computational complexity. We employ a rate-adaptive non-binary LDPC coding scheme which makes use of non-binary repetitions. While this coding scheme is particularly well-suited for adaptive IR-HARQ, we note that the presented analysis can be applied to any other channel code which employs soft decoding.

In this paper, we discuss the combination of non-binary channel coding with higher-order modulation and MIMO transmission in the form of spatial multiplexing. In addition to the benefits of non-binary LDPC codes on the AWGN channel, we identify an inherent advantage for non-binary coding in multiple antenna schemes. By comparing binary and q-ary information processing at the receiver, we highlight the intrinsic advantages of non-binary coding. A performance comparison based on simulation results shows that, at similar system complexity, non-binary information processing can actually outperform the Shannon limit of its binary counterpart.

This paper considers a flexible frequency-selective link adaptation scheme for dynamic scheduling systems. Adaptation is performed based on mutual information metrics imposing no constraints on the scheduling and resource allocation. The proposed bit loading algorithm adjusts the codeword length to the available resource units such that codewords may be transmitted over several slots. Simulation results confirm the flexibility of the proposed algorithm which works irrespective of packet and slot lengths and yields a throughput close to the optimum.

We consider the performance of adaptive coding and modulation (ACM) over a fading channel for the case that the transmitter has only partial channel state information (CSI). We evaluate the degradation due to the partial CSI in terms of additionally required SNR by simulations and an analytical approximation. Then, we propose an ACM scheme with fast link-level retransmissions based on cyclic incremental redundancy and compare its performance to an equivalent scheme based on Chase combining. For both HARQ (hybrid automatic repeat request) schemes, we develop an analytical approximation for the throughput and the delay.

In this paper, we discuss the achievable rate regions for the uplink of an OFDMA system. The capacity region is computed for realistic channel models, exploiting a recent generalization of the well-known iterative water-filling algorithm. We then invoke the important constraint of exclusive user allocation per subchannel and approximate the corresponding capacity region. Apart from considering the capacity regions, we also compute the rate regions which can be achieved with the link adaptation scheme of a 4G system proposal and consider a low-complexity alternative. Finally, we outline the impact of some popular scheduling policies on the achieved rates.

The performance of bit-interleaved coded modulation with iterative detection (BICM-ID) depends strongly on the chosen constellation mapping. In this paper, we present an EXIT chart analysis of a number of mappings that have been designed especially for BICM-ID. This analysis reveals that all these mappings inevitably yield a bit error rate floor, which cannot be overcome by increasing the number of iterations or other measures taken at the receiver side. In order to remove this error floor, we introduce an inner code based on differential encoding with code doping. This coding scheme is of low complexity and introduces no additional redundancy. Two detection schemes of different complexity and similar performance are presented. This enhanced BICM scheme is applied to V-BLAST and a new concept to iteratively mitigate the multi-stream interference is presented

We present a low-complexity combination of a BLAST-like MIMO system and bit-interleaved coded modulation with iterative decoding (BICM-ID). We present a method to exploit soft information stemming from the outer decoder to mitigate the influence of multistream interference. Furthermore, we introduce an inner code to remove the error floor which is normally present in BICM-ID systems. This code is of rate one and has memory one; it thus adds no redundancy and only very little complexity. Both schemes are evaluated in the EXIT chart and with BER simulations.

In this paper, we extend the iterative demapping technique, also known as turbo demodulation, to OFDM.We first introduce an inner code which serves to remove the error floor, which is present in current iterative demapping schemes. This technique is then applied to OFDM with cyclic prefix of zero-padding. Using the EXIT chart, we illustrate the performance differences of various mappings and design a low-complexity inner coding scheme based on differential encoding with code doping. It is shown that this scheme removes the error floor without altering the code rate and while adding very little complexity.

In this paper we present a novel and computationally efficient waterfilling algorithm for multiuser OFDM. This algorithm is based on the multiuser waterfilling theorem and determines the subcarrier allocation for a multiple access OFDM system. This approach maximizes the total bitrate under the constraints of user-individual power budgets. Once the subcarrier allocation has been established, the bit and power allocation for each user can be determined with a single-user bitloading algorithm, for which several implementations can be found in the literature. The presented iterative algorithm performs well, also with a high number of subchannels.

The design of optimum pulses for digital multicarrier offset-QAM (MC-OQAM) is presented. The impulses are designed as finite duration pulses with maximum signal energy in one subcarrier's frequency band. The intersymbol and intercarrier interference is minimized. The solution is obtained by expanding the impulses into finite-length discrete prolate spheroidal sequences. The design method, optimum impulses and simulation results are presented. With this technique, more than 95% of the signal energy can be concentrated in the frequency band of one subcarrier and the out-of-band spectral parts fall off very rapidly in comparison with rectangular pulses used by conventional OFDM systems. Thus, the presented multicarrier system provides much less spectral overlap between modulated subcarriers and is therefore much less susceptible against frequency-selective interference.