Uncoded Case Research Articles

Massive Access in Media Modulation Based Massive Machine-Type Communications

The massive machine-type communications (mMTC) paradigm based on media modulation in conjunction with massive multi-input multi-output base stations (BSs) is emerging as a viable solution to support the massive connectivity for the future Internet-of-Things, in which the inherent massive access at the BSs poses significant challenges for device activity and data detection (DADD). This paper considers the DADD problem for both uncoded and coded media modulation based mMTC with a slotted access frame structure, where the device activity remains unchanged within one frame. Specifically, due to the slotted access frame structure and the adopted media modulated symbols, the access signals exhibit a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">doubly structured sparsity</i> in both the time domain and the modulation domain. Inspired by this, a doubly structured approximate message passing (DS-AMP) algorithm is proposed for reliable DADD in the uncoded case. Also, we derive the state evolution of the DS-AMP algorithm to theoretically characterize its performance. As for the coded case, we develop a bit-interleaved coded media modulation scheme and propose an iterative DS-AMP (IDS-AMP) algorithm based on successive inference cancellation (SIC), where the signal components associated with the detected active devices are successively subtracted to improve the data decoding performance. In addition, the channel estimation problem for media modulation based mMTC is discussed and an efficient data-aided channel state information (CSI) update strategy is developed to reduce the training overhead in block fading channels. Finally, simulation results and computational complexity analysis verify the superiority of the proposed DS-AMP algorithm over state-of-the-art algorithms in the uncoded case. Also, our results confirm that the proposed SIC-based IDS-AMP algorithm can enhance the data decoding performance in the coded case and verify the validity of the proposed data-aided CSI update strategy.

Cooperative Caching for Ultra-Dense Fog-RANs: Information Optimality and Hypergraph Coloring

This work considers cache placement for ultra-dense fog radio access networks (F-RANs). In an F-RAN, the fog access points (F-APs) form overlapping clusters based on their geographical locations. A cluster of F-APs then acts as a distributed cache to cooperatively serve user requests. The fronthaul traffic minimization problem is formulated in information-theoretic terms. For the k-association networks, cache placement can be optimized by concatenating an MDS code with a repetition code. By repeating the same packet in some F-APs, multicasting over the fronthaul link can be done in cache placement, which saves energy and bandwidth. Such an idea is applied to both uncoded and coded caching schemes based on hypergraph coloring. Their associated optimization problems are shown to be NP-complete. For the uncoded case, a suboptimal algorithm is proposed, which carefully repeats the subfiles. For the coded case, a heuristic algorithm that minimizes the field size requirement of the MDS repetition scheme is proposed. Simulation results demonstrate the outstanding performance of the proposed uncoded and coded caching schemes during both the cache placement phase and content delivery phase in reducing fronthaul traffic load and energy consumption.

Golden Coded GFDM for 5G Communication

The 5th Generation (5G) of wireless communication will be heterogeneous to support various traffic types and applications. Generalized Frequency Division Multiplexing (GFDM) is a 5G non-orthogonal waveform contender that offers scalable and spectrally compliant air interface which addresses the needs of 5G requirements. To aid the demand of high-capacity and reliable transmission, multiple antenna techniques are relied upon. In this work, the 5G modulation scheme GFDM is combined with a full rate Space–Time Block Code (STBC) with nonvanishing determinant called Golden Codes to exploit the diversity to the fullest. The proposed work is implemented in a real-time SDR test-bed called Wireless Open Access Research Platform (WARP). The proposed work is compared with 4G OFDM modulation in both Golden Coded and Uncoded case. The performance is assessed in terms of BER and Capacity/Bandwidth resolution. From the investigations, it is seen that the BER performance of Golden Coded GFDM outperforms the Uncoded GFDM by 3 dB SNR gain and attains a near-equal performance as OFDM. Also, it is evident from the analysis that, there is a 3.5 bps/Hz gain in capacity when compared to OFDM.

High-speed and reliable Underwater Wireless Optical Communication system using Multiple-Input Multiple-Output and channel coding techniques for IoUT applications

In this paper, we investigate the performance of an Underwater Wireless Optical Communication (UWOC) system employing on–off keying modulation at a data-rate of 500 Mbps over a link-range of 30 m. Transmit/receive diversity schemes, namely Multiple-Input to Single-Output (MISO), Single-Input to Multiple-Output (SIMO) and Multiple-Input to Multiple-Output (MIMO) techniques with and without RS-coding have been employed to mitigate the effects of weak oceanic turbulence and beam attenuation. The novel closed-form analytical Bit Error Rate (BER) expressions of Single-Input to Single-Output (SISO), SIMO, MISO and MIMO links for un-coded and RS-coded cases have been computed using the hyperbolic tangent distribution and validated with Monte-Carlo simulation results. The obtained BER results show that the use of (63,51) RS-coded 4 × 5 MIMO UWOC system offers at-least 35 dB of transmit power gain compared with the un-coded SISO UWOC system at a BER of 10−5. Emerging technologies like the fifth-generation (5G) networks and the Internet of Underwater Things (IoUT) will have a high impact on UWOC as these systems require a high degree of information integrity, high data rates and energy efficiency when employed in conjunction with data transfer between underwater vehicles and objects. The proposed RS-coded MIMO UWOC system offers high reliability and power efficiency and it has the potential to be gainfully employed in IoUT applications.

On Orthogonal AMP in Coded Linear Vector Systems

Linear minimum mean square error (LMMSE) estimation based turbo detection has been extensively studied for coded linear systems since the seminal work of Wang and Poor (WP). The WP algorithm operates iteratively between a linear detector (LD) and a nonlinear detector (NLD): the LD suppresses the interference based on LMMSE filtering, and the NLD decodes the data by treating the output of the LD as an observation from an additive white Gaussian noise (AWGN) channel. In WP, the messages exchanged between LD and NLD are required to be extrinsic . For the NLD, the extrinsic message comes from the constraint imposed on feedforward error correction (FEC) codes. Therefore, WP does not work in an un-coded linear system. Recently, we proposed an orthogonal approximate message passing (OAMP) algorithm, which only requires the input/output error terms of LD and NLD to be orthogonal . We conjectured that for un-coded linear systems that involve certain large random matrices, the dynamics of OAMP can be accurately characterized by state evolution (SE). In this paper, we consider a coded linear system and develop an extrinsic message aided OAMP (EMA-OAMP) algorithm. Similar to the un-coded case, EMA-OAMP relaxes the requirements on output messages to be orthogonal instead of extrinsic. We derive an SE procedure to characterize the performance of OAMP in coded systems. We conjecture that this SE procedure is accurate, which is verified by simulation results. Under this conjecture, we show that EMA-OAMP can outperform WP under certain standard assumptions for iterative decoding. Extensive simulations results are provided to verify the advantages of OAMP in coded MIMO systems.

IMPROVING BER PERFORMANCE AND SECURITY IN PLC CHANNEL USING OSTBC, CONVOLUTIONAL CODING AND INTERLEAVING WITH HYBRID SDES-AES ENCRYPTION

This paper aims to improve data security and BER performance in the Power Line Communication channel by using encryption and channel coding techniques. In particular, improvement in BER performance has been obtained while using OSTBC rather than STBC as compared to the results obtained in a previous work. The improved system has been extended to include data security in the PLC channel. In this respect, a Hybrid SDES-AES encryption scheme has been developed. The BER performance of the Hybrid SDES-AES encryption in the PLC channel has been improved by using Convolutional coding, Interleaving and OSTBC. A performance improvement of 11.8 dB has been obtained at a BER of 3×10−5 when compared with the Uncoded Hybrid Encryption case.

A Low-Complexity Detection Algorithm for Uplink Massive MIMO Systems Based on Alternating Minimization

In this letter, we propose an algorithm based on the alternating minimization technique to solve the uplink massive multiple-input multiple-output (MIMO) detection problem. The proposed algorithm is specifically designed to avoid any matrix inversion and any computations of the Gram matrix at the receiver. The algorithm provides a lower complexity compared to the conventional minimum mean square error detection technique, especially when the total number of user equipment antennas (across all users) is close to the number of base station antennas. The idea is that the algorithm re-formulates the maximum-likelihood detection problem as a sum of convex functions based on decomposing the received vector into multiple vectors. Each vector represents the contribution of one of the transmitted symbols in the received vector. Alternating minimization is used to solve the new formulated problem in an iterative manner with a closed-form solution update in every iteration. Simulation results demonstrate the efficacy of the proposed algorithm in the uplink massive MIMO setting for both coded and uncoded cases.

Robust Single-Carrier Frequency-Domain Equalization for Broadband MIMO Systems With Imperfect Channel Estimation

Single-carrier frequency-domain equalization (SC-FDE) with multi-input multi-output (MIMO) has been recognized as an alternative technology to orthogonal frequency-division multiplexing with MIMO for broadband wireless communication systems because of its single carrier transmission advantages. Conventional SC-FDE MIMO schemes are designed under the assumption of perfect channel estimation. In this paper, we investigate the robust SC-FDE MIMO design for systems with imperfect channel estimation. Based on a statistical model for channel estimation, the optimal equalization coefficients for the robust SC-FDE MIMO schemes with both parallel interference cancellation and successive interference cancellation (SIC) are derived with the objective of minimizing the sum of the multiple data streams’ mean square errors (sum-MSE). We propose an optimal ordering algorithm in the sense of minimum sum-MSE for the SC-FDE MIMO scheme with SIC, and further propose a low complexity sub-optimal ordering algorithm. The bit-error-rate (BER) performance in the uncoded case is analyzed and a tight BER approximation is derived. Numerical results show that the proposed robust SC-FDE MIMO schemes achieve 1.5dB~4dB gains in $ E_{b}/N_{0}$ over the conventional non-robust schemes.

Noncoherent Short Packet Detection and Decoding for Scatter Radio Sensor Networking

Scatter radio, i.e., communication by means of reflection, has been recently proposed as a promising technology for low-power wireless sensor networks (WSNs). Specifically, this paper offers noncoherent receivers in scatter radio frequency-shift keying, for either channel-coded or uncoded scatter radio reception, in order to eliminate the need for training bits of coherent schemes (for channel estimation) at the packet preamble. Noncoherent symbol-by-symbol and sequence detectors based on hybrid composite hypothesis test (HCHT) and generalized likelihood-ratio test, for the uncoded case and noncoherent decoders based on HCHT, for small block-length channel codes, are derived. Performance comparison under Rician, Rayleigh, or no fading, taking into account fixed energy budget per packet is presented. It is shown that the performance gap between coherent and noncoherent reception depends on whether channel codes are employed, the fading conditions (e.g., Rayleigh versus Rician versus no fading), as well as the utilized coding interleaving depth; the choice of one coding scheme over the other depends on the wireless fading parameters and the design choice for extra diversity versus extra power gain. Finally, experimental outdoor results at 13-dBm transmission power corroborate the practicality of the proposed noncoherent detection and decoding techniques for scatter radio WSNs.

Joint algebraic coded modulation and lattice‐reduction‐aided preequalisation

Lattice-reduction-aided (LRA) preequalisation for the multiple-input/multiple-output broadcast channel has most often been considered for the uncoded case so far. However, recent advantages in the closely related field of integer-forcing equalisation, where the cancellation of the multiuser interference and the channel coding are combined, create doubt to this separated point of view. In this Letter, the philosophy of matching both the channel code and the complex-valued signal constellation to the same finite-field arithmetic is proposed. The consequences on the factorisation task present in LRA preequalisation are discussed and covered by numerical performance evaluations based on non-binary low-density parity-check codes.

On the Optimization of a PSP-Based CPM Detection

This paper deals with a reduced-complexity per survivor processing-based CPM demodulation. It relies on a trellis with reduced state number and defined from a rational modulation index possibly different from the transmit modulation index and referred to as virtual receiver modulation index. The virtual receiver modulation index should be chosen so as to achieve a tradeoff between error-rate performance and complexity reduction. The main purpose of this paper is the choice of the virtual receiver modulation index. It gives guidelines to discard the values of the virtual receiver modulation index, that degrade the error-rate performance. Two criteria are used. The first one considers the uncoded CPM case and is based on an approximation of the minimal Euclidean distance. The second one is related to the bit interleaved coded CPM case and resorts to an EXIT chart to analyze the convergence of the iterative receiver.

Performance Analysis of MIMO Schemes in 3GPP Long Term Evolution System

This paper, presents evaluation and analysis of the performance for multiple-input multiple-output (MIMO) schemes in the 3GPP long term evolution (LTE) system. Three performance metrics are considered for the analysis and evaluation, namely, average BER, average channel capacity and average throughput of the system for two different MIMO schemes as defined in LTE. Using the numerical results obtained from the mathematical expressions derived in the paper, we compare the presented schemes and show their significant advantages. Monte-Carlo simulation results of the LTE system are also provided to verify the accuracy of the mathematical analysis. The results for the average throughput of the considered MIMO schemes in LTE are presented for the un-coded case as well as for the coded-case in practical LTE scenarios. In addition, for the sake of comparison, the theoretical capacity limit of the system is also shown.

A Cross-Layer Optimization Approach for Lower Layers of the Protocol Stack in Sensor Networks

A cross-layer optimization approach for the physical and medium access control layers of wireless sensor networks is introduced in this article. This approach includes a Markov chain model, simulations, and analytical derivations that are applied to the analysis of sensor networks using impulse radio ultra-wideband signals with noncoherent energy detection. This type of communication system has low-power transmission requirements and noise like signal characteristics with low interference to other wireless systems. The energy efficiency of different Reed-Solomon code rates and uncoded case are studied in a star topology network, where slotted Aloha, as defined in the IEEE 802.15.4a standard, is used as the medium access protocol. Analytical and simulation results clearly show the potential energy gains that can be achieved with the proposed optimization approach that can be also used in the evaluation and optimization of other combinations of physical and medium access control protocols.

FemtoCaching: Wireless Content Delivery Through Distributed Caching Helpers

Video on-demand streaming from Internet-based servers is becoming one of the most important services offered by wireless networks today. In order to improve the area spectral efficiency of video transmission in cellular systems, small cells heterogeneous architectures (e.g., femtocells, WiFi off-loading) are being proposed, such that video traffic to nomadic users can be handled by short-range links to the nearest small cell access points (referred to as “helpers”). As the helper deployment density increases, the backhaul capacity becomes the system bottleneck. In order to alleviate such bottleneck we propose a system where helpers with low-rate backhaul but high storage capacity cache popular video files. Files not available from helpers are transmitted by the cellular base station. We analyze the optimum way of assigning files to the helpers, in order to minimize the expected downloading time for files. We distinguish between the uncoded case (where only complete files are stored) and the coded case, where segments of Fountain-encoded versions of the video files are stored at helpers. We show that the uncoded optimum file assignment is NP-hard, and develop a greedy strategy that is provably within a factor 2 of the optimum. Further, for a special case we provide an efficient algorithm achieving a provably better approximation ratio of 1-(1-1/d )d, where d is the maximum number of helpers a user can be connected to. We also show that the coded optimum cache assignment problem is convex that can be further reduced to a linear program. We present numerical results comparing the proposed schemes.

Channel Coding Increases the Achievable Rate of the Cognitive Networks

In this letter, we investigate employing Trellis Coded Modulation (TCM) in an Orthogonal Frequency Division Multiple Access (OFDMA) based secondary system in an underlay cognitive radio network. While it is expectable for channel coding to improve the performance in the secondary service compared to the uncoded case at the expense of rate reduction, our results indicate that the benefits of such utilization is beyond expectation. In fact we show that for a given bandwidth and bit error rate performance, the coded scheme not only requires less average transmit power per subcarrier, but it also provides a significantly higher sum-rate compared to the uncoded case. This result is against the well-known property of channel coding in conventional communication systems where we sacrifice effective date rate to reduce the required power for a given bit error rate. This is due to the fact that using TCM in the secondary system, we successfully transmit bits with a lower transmit power. Having a transmission with lower transmit power, we would be able to transmit with a higher bit rate in the secondary system and still meet the interference threshold requirements in the primary network. Total rate is increased if the increase due to lower transmit power beats the decrease caused by coding. Our simulation results show that this is indeed the case for TCM-OFDMA secondary system.

Iterative Decision-Directed Joint Frequency Offset and Channel Estimation for KSP-OFDM

We propose an iterative decision-directed joint frequency offset (FO) and channel estimation algorithm in a known symbol padding (KSP) orthogonal frequency division multiplexing (OFDM) system, where the guard interval is filled with pilot symbols. Besides those time domain pilot symbols, some additional pilot symbols are transmitted on the pilot carriers. The decision-directed algorithm is initialized by pilot-aided FO estimation without channel knowledge. We propose a possible initialization algorithm that operates in the frequency domain (FD). After the initialization phase, the iterative decision-directed estimation algorithm is applied. For the channel estimation step, an existing pilot-aided channel estimation algorithm is extended to a decision-directed algorithm which uses the Fast Fourier Transform outputs at both the pilot and data carrier positions. For the uncoded case, the proposed iterative decision-directed joint FO and channel estimation algorithm reaches the bit error rate performance of a receiver with perfect synchronization and perfect channel knowledge. For a coded system, there is small loss in performance of less than 1 dB when our proposed algorithm is applied compared to a receiver with perfect knowledge about the FO and the channel.

Impact of Different Spreading Codes Using FEC on DWT Based MC-CDMA System

The effect of different spreading codes in DWT based MC-CDMA wireless communication system is investigated. In this paper, we present the Bit Error Rate (BER) performance of different spreading codes (Walsh-Hadamard code, Orthogonal gold code and Golay complementary sequences) using Forward Error Correction (FEC) of the proposed system. The data is analyzed and is compared among different spreading codes in both coded and uncoded cases. It is found via computer simulation that the performance of the proposed coded system is much better than that of the uncoded system irrespective of the spreading codes and all the spreading codes show approximately similar nature for both coded and uncoded in all modulation schemes.

Multiple Beamforming with Perfect Coding

Perfect Space-Time Block Codes (PSTBCs) achieve full diversity, full rate, nonvanishing constant minimum determinant, uniform average transmitted energy per antenna, and good shaping. However, the high decoding complexity is a critical issue for practice. When the Channel State Information (CSI) is available at both the transmitter and the receiver, Singular Value Decomposition (SVD) is commonly applied for a Multiple-Input Multiple-Output (MIMO) system to enhance the throughput or the performance. In this paper, two novel techniques, Perfect Coded Multiple Beamforming (PCMB) and Bit-Interleaved Coded Multiple Beamforming with Perfect Coding (BICMB-PC), are proposed, employing both PSTBCs and SVD with and without channel coding, respectively. With CSI at the transmitter (CSIT), the decoding complexity of PCMB is substantially reduced compared to a MIMO system employing PSTBC, providing a new prospect of CSIT. Especially, because of the special property of the generation matrices, PCMB provides much lower decoding complexity than the state-of-the-art SVD-based uncoded technique in dimensions 2 and 4. Similarly, the decoding complexity of BICMB-PC is much lower than the state-of-the-art SVD-based coded technique in these two dimensions, and the complexity gain is greater than the uncoded case. Moreover, these aforementioned complexity reductions are achieved with only negligible or modest loss in performance.

A Comparison Study Between Pre-Equalization Schemes for Single and Multi Carrier Modulation Systems

In this paper, frequency domain pre-equalization (Pre-FDE) is developed for broadband cyclic prefix-code division multiple access (CP-CDMA) as a single carrier transmission scheme, and for multi carrier-CDMA (MC-CDMA) and orthogonal frequency division multiplexing (OFDM) as multi carrier transmission schemes. A comparison study is held between these schemes and the traditional equalization schemes. Experimental results show that pre-equalization improves significantly the performance of the single and multi carrier communication systems with a very low complexity at the receiver. The comparative study between MIMO pre-equalization for single carrier systems and for multi carrier systems shows that MIMO pre-equalization for single carrier systems outperforms that for multi carrier systems in terms of bit error rate (BER) performance since single carrier transmission has more frequency diversity than multi carrier transmission in the uncoded case.

Partially Coherent EGC Reception of Uncoded and LDPC-Coded Signals over Generalized Fading Channels

This paper studies the bit-error rate (BER) performance of partially coherent equal-gain combining reception of uncoded and low-density parity-check (LDPC)-coded binary and quaternary phase-shift keying signals over generalized α − μ fading channels. For the uncoded signal detection case the obtained numerical and simulation results illustrate the BER performance degradation due to the imperfect reference signal recovery, receiver unbalancing and fading. It is demonstrated that imperfect cophasing causes an irreducible BER performance. Furthermore, we design large girth quasi-cyclic LDPC code with high code rate, suitable for use in communications over generalized fading channels. The proposed LDPC code does not exhibit the error floor phenomena, in the region of interest, even in the presence of imperfect cophasing and receiver unbalances, and outperforms standard convolutional code of lower code rate in the observed impairments. The effects of number of iterations in decoding algorithm and codeword length on BER performance are also investigated.