Nikola Serafimovski

Generalised spatial modulation

In this paper, a generalised technique for spatial modulation (SM) is presented. Generalised spatial modulation (GSM) overcomes in a novel fashion the constraint in SM that the number of transmit antennas has to be a power of two. In GSM, a block of information bits is mapped to a constellation symbol and a spatial symbol. The spatial symbol is a combination of transmit antennas activated at each instance. The actual combination of active transmit antennas depends on the random incoming data stream. This is unlike SM where only a single transmit antenna is activated at each instance. GSM increases the overall spectral efficiency by base-two logarithm of the number of antenna combinations. This reduces the number of transmit antennas needed for the same spectral efficiency. The performance of GSM is analysed in this paper, and an upper bound on the bit-error-ratio (BER) performance is derived. In addition, an algorithm to optimise the antenna combination selection is proposed. Finally, the performance of GSM is validated through Monte Carlo simulations. The results are compared with traditional SM. It is shown that for the same spectral efficiency GSM performs nearly the same as SM, but with a significant reduction in the number of transmit antennas.

Practical Implementation of Spatial Modulation

In this paper, we seek to characterize the performance of spatial modulation (SM) and spatial multiplexing (SMX) with an experimental testbed. Two National Instruments (NI) PXIe devices are used for the system testing: one for the transmitter and one for the receiver. The digital signal processing (DSP) that formats the information data in preparation for transmission is described, along with the DSP that recovers the information data. In addition, the hardware limitations of the system are also analyzed. The average bit-error ratio (ABER) of the system is validated through both theoretical analysis and simulation results for SM and SMX under the line-of-sight (LoS) channel conditions.

Multiple access spatial modulation

In this study, we seek to characterise the behaviour of Spatial modulation (SM) in the multiple access scenario. By only activating a single transmit antenna for any transmission, SM entirely avoids inter-channel interference, requires no synchronisation between the transmit antennas and a single radio frequency chain at the transmitter. Most contributions thus far have only addressed aspects of SM for a point-to-point communication system. We propose a maximum-likelihood (ML) detector which can successfully decode incoming data from multiple simultaneous transmissions and does not suffer from the near-far problem. We analyse the performance of the interference-unaware and interference-aware detectors. We look at the behaviour of SM as the signal-to-interference-plus-noise ratio goes to infinity and compare it to the complexity and cost equivalent single-input-multiple-output (SIMO) system. Two systems are considered to be equivalent in terms of complexity if their respective detection algorithms are of the same order inO(·)notation. Simulation results show that the interference-aware SM detector performs better than the complexity equivalent multi-user ML-SIMO detector by at least 3 dB at an average bit-error-ratio of 10−3.

Dual-Hop Spatial Modulation (Dh-SM)

In this paper, we introduce Dual-hop Spatial Modulation (Dh-SM). We look at the effect that Dh-SM has on the required signal to noise ratio (SNR) at the destination and how it can help alleviate the multi-hop burden. Initial bit-error-ratio (BER) results comparing the performance of Dh-SM with orthogonal decode-and-forward (DF) are presented where Dh-SM is shown to have up to a 10 dB SNR advantage.

Fractional frequency reuse in optical wireless cellular networks

Interference coordination in optical wireless cellular networks using different frequency reuse techniques are discussed and compared in this paper. On the one hand, full frequency reuse maximises the system throughput at the cost of poor cell-edge user performance. On the other hand, cluster-based static resource partitioning offers good cell-edge user performance at the cost of low system throughput. Fractional frequency reuse (FFR) is introduced as a compromise between cell-edge user performance and the system throughput with low system complexity. Simulation results show that a guaranteed user throughput of 5.6 Mbps and an average area spectral efficiency (ASE) of 0.3389 bps/Hz/m2 are achieved by the FFR optical wireless system with appropriate power control factors. These results show considerable throughput improvement compared to both benchmark systems. It is also shown that by adjusting the LED transmission optical power of a system using visible light spectrum, the illumination requirement for an office room can be satisfied without extra lighting facilities.

A European view on the next generation optical wireless communication standard

Optical wireless technology uses light for mobile communications. The idea is to simultaneously combine the illumination provided by modern high-power light-emitting diodes (LEDs) with high-speed wireless communications. There have been numerous practical demonstrations of this concept, and the technology is now well matured to be deployed in practice. Independent market analysts forecast a high-volume market for mobile communication devices connected to the ubiquitous lighting infrastructure. This paper aims to make optical and wireless industries aware of the requirement for standardization in this area. The authors present the view of the European COST 1101 research network OPTICWISE towards a next-generation optical wireless standard aiming at data rates from 1 Mbit/s to 10 Gbit/s. Besides key technical insights, relevant use cases and main features are described that were recently adopted by the IEEE 802.15.7r1 working group. Moreover, a channel model is introduced to enable assessment of technical proposals.

2-User multiple access spatial modulation

Spatial modulation (SM) is a recently proposed approach to multiple-input-multiple-output (MIMO) systems which entirely avoids inter-channel interference (ICI) and requires no synchronisation between the transmit antennas, while achieving a spatial multiplexing gain. SM allows the system designer to freely trade off the number of transmit antennas with the signal constellation. Additionally, the number of transmit antennas is independent from the number of receive antennas which is an advantage over other multiplexing MIMO schemes. Most contributions thus far, however, have only addressed SM aspects for a point-to-point communication systems, i.e. the single-user scenario. In this work we seek to characterise the behaviour of SM in the interference limited scenario. The proposed maximum-likelihood (ML) detector can successfully decode incoming data from multiple sources in an interference limited scenario and does not suffer from the near-far problem.

Angle Diversity for an Indoor Cellular Visible Light Communication System

In this paper, we investigate the benefits of an angle diversity receiver (ADR) in an indoor cellular optical wireless communications (OWC) network. As the ADR consists of multiple photodiodes (PDs), a proper signal combining scheme is essential to optimise the system performance. Therefore, three different combination schemes, the equal gain combining (EGC), the select best combining (SBC) and the maximum ratio combining (MRC), are investigated. The results indicate that the ADR significantly outperforms the single-PD receiver in terms of both signal to interference plus noise ratio (SINR) and area spectral efficiency (ASE). In particular, the ADR implementing the MRC scheme achieves the best performance, where over 40 dB SINR improvement is attained compared to the single-PD receiver.

Secrecy Capacity of Space Keying with Two Antennas

Spatial modulation (SM) and space shift keying (SSK) use only one out of several transmit antennas at a time to transmit data via an antenna index. In such a system, the information is encoded by exploiting channel randomness i.e. the fact that channels between different transmit and receive antennas are random. This difference is used to distinguish among the transmit antennas. While SSK uses only antenna index to transmit data, SM also uses ordinary signal modulation. In wireless secrecy systems, one of the key performance measures is secrecy capacity. It specifies the rate at which the transmitter can communicates on the main link to the desired receiver while this information cannot be decoded by the eavesdropper. We investigate SM and SSK in the context of wireless secrecy capacity when the underlying modulation and the difference between the legitimate and eavesdropper signal to noise ratios (SNRs) are varied.

System Spectral Efficiency Analysis of a 2-Link Ad Hoc Network

This paper analyzes the system spectral efficiency of a 2-link ad hoc network. The analysis shows that there are exactly three operating points that maximize system capacity: either both links transmit with maximum power simultaneously; or one single link transmits with maximum power while the other is silent. The impact of the scheduling policy on the system spectral efficiency is also studied: simultaneous transmission or sequential access where the two links share the medium by dedicated time/frequency slots without causing interference. An exhaustive numerical search over a wide range of pathloss parameters shows that sequential transmission is superior to simultaneous transmission in about two third of the cases. Even when simultaneous transmission outperforms sequential transmission, the gains are typically not substantial. Furthermore, we show that in case of simultaneous transmission power control causes only marginal degradation in terms of system spectral efficiency, while transmitting with maximum power pays off for sequential transmission. This highlights the importance of the joint optimization of power and rate adaptation together with scheduling for power constraint ad hoc networks.