Interference analysis and MUI-cancellation in DCO-OFDMA-based IM/DD systems for VLC

A novel passive optical network (PON) architecture based on optical orthogonal frequency division multiple access (OFDMA) technologies is presented. Two potential medium access control (MAC) methods namely dynamic circuit transmission and fixed burst transmission are investigated.

Performance analysis of colour coded multiple access (CCMA) orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) System is discussed in this paper. First, characteristics of optical OFDM are studied. Second, CCMA is achieved using three laser diodes (LD): red, green and blue LDs. Finally, OFDM-modulated signals are optically modulated with red, green and blue LDs (RGB LDs). Then these three optical signals are combined together to form white light which illuminates as well as provides high-speed data transmission. The performance of the proposed CCMA OFDM VLC system is studied using constellation diagrams, signals and spectrum comparisons. The system is simulated for the data rate of 10 Gbps.

In uplink orthogonal frequency division multiple access (OFDMA), carrier frequency offsets (CFO) and/or timing offsets (TO) of other users with respect to a desired user can cause significant multiuser interference (MUI). In this paper, we derive analytical bit error rate (BER) expressions that quantify the degradation of BER due to the combined effect of both CFOs as well as TOs; such an analytical BER derivation has not been reported so far for uplink OFDMA in the presence of CFOs and TOs. For the case when the desired user is perfectly frequency/time aligned (and other users have non-zero CFOs/TOs), we obtain an exact closed-form expression for the BER. For the case when the desired user also has non-zero CFO/TO, we obtain an approximate BER expression involving a single integral. Analytical and simulation results are shown to match quite well.

One of the major drawbacks of the orthogonal frequency division multiple access (OFDMA) system is the multi-user interference (MUI) induced by the carrier frequency offsets (CFOs). In sub-band based OFDMA systems, users occupy consecutive and non-overlapping frequency sub-bands. The pilots are usually placed on the edges of a sub-band for channel estimation. However, the channel estimation performance is seriously degraded by the MUI. Traditionally, the MUI is alleviated by inserting a guard sub-carrier between adjacent users. In this paper, a novel pilot architecture is proposed, where three pilots are placed on each edge of a sub-band and pilots of adjacent users are overlapped. The proposed architecture has the same bandwidth efficiency as that of the conventional guard sub-carrier insertion scheme and provides better channel estimation performance and MUI reduction.

A flexible optical OFDMA-PON upstream scheme based on modulation format conversion technique

This paper addresses the statistical analysis of Transceiver Phase Noise (PHN) effect on Orthogonal Frequency Division Multiple Access (OFDMA) Uplink system performance for arbitrary subcarrier mapping. In most of the previous publications Complex Gaussian distribution of Inter Carrier Interference (ICI) was assumed, however in this paper we derive a closed form expression for the signal-to-interference+ noise ratio (SINR) without such restriction and then analyse it as a function of critical system parameters. This improved evaluation stringently specifies the plausible acceptable PHN characteristics for a certain OFDMA Uplink system and explains the serious under specification of Local Oscillator (LO) with Gaussian approximation.

Device-to-device (D2D) communication is one of the promising technology of the fifth-generation (5G) network. In D2D, the devices are in close proximity to each other communicate directly with or without depending upon the base station (BS), resulting in large gain, low latency, and high energy efficiency. Also, it improves the spectral efficiency by sharing the spectrum resources with cellular mobile users (CMUs). Despite these advantages, co-channel interference and eavesdropping attack on the D2D links are two major challenges. To overcome these issues, we used the power domain non orthogonal multiple access (PDNOMA) techniques with the D2D mobile groups (DMGs) under the social-domain scenario. The successive interference cancellation technique of PD-NOMA in the DMGs mitigate the intra-user and co-channel interference among the D2D receivers (DDRs), resulting in an increase in signal to interference noise ratio (SINR) and better quality of services. Furthermore, to improve the spectral efficiency, and reduce the security risk of the eavesdropper on the DMGs over each resource block (RB) in the presence of dynamic channel environment of imperfect channel state information, we used the coalition game approach. The simulated results show the proposed scheme achieves 5.5% and 27.77% higher sum rate and ensure 8.3% and 41.6% higher information secrecy as compared to first-order algorithm (FOA) and orthogonal frequency division multiple access (OFDMA) schemes.

In uplink orthogonal frequency division multiple access (OFDMA) systems, multiuser interference (MUI) occurs due to different carrier frequency offsets (CFO) of different users at the receiver. In this paper, we present a minimum mean square error (MMSE) based approach to MUI cancellation in uplink OFDMA. We derive a recursion to approach the MMSE solution. We present a structure-wise and performance-wise comparison of this recursive MMSE solution with a linear PIC receiver as well as other detectors recently proposed in the literature. We show that the proposed recursive MMSE solution encompasses several known detectors in the literature as special cases.

For multi-antenna Orthogonal Frequency-Division Multiple Access (OFDMA) based multicell networks, the channel state information (CSI) of all users is required to share among base stations in order to perform distributed power allocation. However, the amount of feedback increases with the number of users, base stations, subcarriers and antennas. Therefore, it is important to perform a selection at the user side to reduce the feedback load and the complexity of resource allocation. In this letter, we propose adaptive reduced feedback links by choosing the users based on their approximate signal to interference noise ratio (SINR) and their locations in the cell to satisfy users' rate constraints. We illustrate the performance results of reduced feedback links by employing distributed resource allocation with link adaptation.

In this paper, the performance of parallel interference cancellation (PIC) multi-user detectors in orthogonal frequency division multiple access (OFDMA) mobile communication systems is investigated. In multi-user systems, the multi-user interference (MUI) degraded the system performance, especially in near-far effect environments. An adaptive weight partial PIC (AWPPIC) scheme is proposed to reduce the MUIs and to improve the bit error rate (BER) performance for uplink OFDMA systems. Simulation results show that under the near far problems for block sub carrier assignment (BCA) scheme, the AWPPIC scheme can improve the BER performance no matter what the system load is.

A low complexity iterative equalization technique for OFDMA and SC-FDMA uplink systems with Tx-Rx IQ imbalance and CFO under doubly selective channels

Code division multiple access (CDMA) over frequency-selective fading channels faces challenges in suppressing multiuser interference (MUI), but can also benefit from the channel-induced multipath diversity. On the other hand, uncoded orthogonal frequency division multiple access (OFDMA) is MUI-free by design, but faces challenges arising from the fading-induced loss of multipath diversity. We wed the advantages of CDMA with those of OFDMA. We design a group-orthogonal multi-carrier CDMA (GO-MC-CDMA) scheme that minimizes MUI subject to the constraint that the full multipath diversity is enabled for all users. Each group of GO-MC-CDMA users shares a properly selected set of system subcarriers. MUI only exists among users in the same small-size group, which renders the application of low-complexity multiuser detection per group practically feasible. Simulation results illustrate the merits of GO-MC-CDMA over competing multi-access alternatives.

With the properties of interference avoidance and the robustness against multipath channels, Orthogonal Frequency Division Multiple Access (OFDMA) has been considered a promising solution to the interference control problem in femtocells. As a multi-carrier transmission technique, OFDMA, however, is highly vulnerable to the Carrier Frequency Offset (CFO). This chapter discusses the challenges of multiple frequency offsets compensation in OFDMA femtocells. A number of multiple frequency offsets compensation algorithms are reviewed and their complexities are discussed in detail. A new approach that exploits the redundancy offered by cyclic prefix is then introduced to enhance the compensation performance. Finally, numerical results are presented to illustrate the performance of different compensation algorithms.

This paper proposes the theoretical derivation method of the Shannon capacity for nonlinearly amplified uplink Orthogonal Frequency Division Multiple Access (OFDMA) in the presence of terminal mobility. In our theoretical derivation, the impact of the intercarrier interference (ICI) arising from terminal mobility as well as the multiuser interference (MUI) caused by nonlinear amplification of the mobile stations (MSs) on OFDMA signals is taken into account. Considering the fact that these interferences differ with the sub-carrier allocation methods such as localized FDMA (LFDMA) and interleaved FDMA (IFDMA), we derive the probability density function (PDF) of the instantaneous signal-to-noise-plus-distortion-plus-interference ratio (SNDIR) for each sub-carrier allocation method. Since the SNDIR is successfully expressed in the closed form, the proposed formula enables us to evaluate the Shannon capacity without conducting time consuming computer simulations.

In this letter, we study the achievable rates adopting two delay-Doppler (DD) domain multiples access (MA) schemes for uplink orthogonal time frequency space (OTFS) transmissions, namely delay division multiple access (DDMA) and Doppler division multiple access (DoDMA). To shed light on the system performance, we establish the achievable rate upper-bounds for both DDMA and DoDMA in comparisons to that of the conventional orthogonal frequency division multiple access (OFDMA). In particular, we show that both DDMA and DoDMA have more robust signal-to-interference-plus-noise ratio (SINR) performances against channel fluctuations compared to OFDMA and this robustness leads to higher achievable rates for both DDMA and DoDMA. To be more specific, we find that the achievable rate upper-bounds for OTFS depend only on the channel fading coefficients of different paths and the multi-user interference (MUI), while the delay and Doppler shifts also have significant impacts on that of the conventional OFDMA. Our simulation results are consistent with our derivations and demonstrate a noticeable improvement of the achievable rates for both DDMA and DoDMA over OFDMA.