In this paper, we present a novel neural architecture for 5G channel estimation (CE), the Recurrent Equivariant UERS Estimation Network (ReQuestNet). It incorporates several practical considerations in wireless communication systems, such as ability to handle variable number of resource block (RB), dynamic number of transmit layers, physical resource block groups (PRGs) bundling size (BS), demodulation reference signal (DMRS) patterns with a single unified model, thereby, drastically simplifying the CE pipeline. Besides it addresses several limitations of the legacy linear minimum mean squared error (MMSE) solutions, for example, by being independent of other reference signals and particularly by jointly processing multiple input multiple output (MIMO) layers and differently precoded channels, unknown at the receiver. ReQuestNet comprises of two sub-units, CoarseNet followed by RefinementNet. CoarseNet performs per PRG, per transmit-receive (Tx-Rx) stream channel estimation, while RefinementNet refines the CoarseNet channel estimate by incorporating correlations across differently precoded PRGs, and correlation across MIMO channel spatial dimensions (cross-MIMO). The simulation results show that ReQuestNet outperforms genie MMSE across various channel profiles as well as unseen channel profiles during training, achieving up to 10dB gain at high signal-to-noise ration (SNR).

Cooperative communication is a promising path to recover from performance anomaly in IEEE 802.11 networks. However, a simple solution for employing multiple relays to enhance the relay link quality has not been proposed. The main obstacle for multiple relay utilization in distributed networks is that synchronizing relay transmissions requires huge signaling overhead. In this paper, we investigate the problem from both a physical-layer and MAC-layer point of view. In the physical layer, a simple, practical solution that provides diversity gain from asynchronous relay transmissions is introduced. In the MAC layer, a rate adaptation algorithm, RA-ARF, that takes the extra relay path into account is discussed, and R-MAC is designed to utilize relays in IEEE 802.11 networks. Our simulation results show considerable improvement in network performance using R-MAC.

Multi-user detection is an efficient approach proposed to boost the spectral efficiency of a wireless communication system. While multi-user detection in synchronous systems or in flat fading environments has been successfully addressed, it is still an open and challenging problem in the practical case of asynchronous MIMO systems employing space-frequency (time) block coding and operating in frequency selective environments. In this paper, we show how the concept of multi-user detection can be efficiently extended to the latter case with a low complexity overhead and a small performance loss compared to the synchronous case.

The use of multiple packet reception (MPR) can alleviate congestion in multi-hop networks and improve network Goodput. However, a sophisticated design is required in order to enable MPR in such networks considering the heterogeneity of transiting packets, both in size and arrival times. In this paper, we introduce a cross-layer MPR-PHY/MAC design suitable for multi-hop ad-hoc networks. Our design identifies three phases of operation tied to the network offered load. Simulation results show that the saturation Goodput of a network using our proposed MPR-PHY/MAC design is better than that of a network using standard IEEE 802.11 PHY and MAC by a factor of at least 50%.

Recent works have considered the feasibility of full duplex (FD) wireless communications in practice. While the first FD system by Choi et.al. relied on a specific antenna cancellation technique to achieve a significant portion of self-interference cancellation, the various limitations of this technique prompted latter works to move away from antenna cancellation and rely on analog cancellation achieved through channel estimation. However, the latter systems in turn require the use of variable attenuator and delay elements that need to be automatically tuned to compensate for the self-interference channel. This not only adds complexity to the overall system but also makes the performance sensitive to wide-band channels. More importantly, none of the existing FD schemes can be readily scaled to MIMO systems.

The use of multiple-packet reception (MPR) in wireless networks is known to improve throughput especially in high-traffic conditions. The lack of synchronization among the nodes in random access systems introduces significant challenges toward the adoption of MPR in the PHY and the MAC design for systems using MPR. In this paper, we propose an asynchronous MPR method for the PHY and also design a compatible random access MAC for wireless local area networks (WLANs). Relying on space-time coding techniques, our MPR method detects multiple asynchronous packets while providing diversity and low bit error rates at the PHY layer. Extending the design of IEEE 802.11, our MPR MAC design encourages simultaneous packet transmissions and handles multiple packet receptions. Simulation results show that the throughput of a WLAN significantly improves in many scenarios of operation using our proposed PHY/MAC MPR framework.

Coping with collisions is one of the biggest challenges in the design of MAC algorithms for wireless networks. Recent advances in MIMO communications have provided the possibility of simple detection of colliding packets. In this paper, we introduce a new MIMO/MPR-aware cross-layer MAC/PHY design that is capable of combating collisions through the use of a multiple packet reception technique. Analytical and simulation results show that the proposed MAC design can considerably improve the throughput of a WLAN operating over lossy links.

Coping with collisions is one of the biggest challenges in the design of MAC algorithms for wireless networks. Recent advances in MIMO communications have provided the possibility of decoding colliding packets. In this paper, we introduce a new MIMO cross-layer MAC/PHY design that is capable of combating collisions through the use of a multiple packet detection technique. Analytical and simulation results show that the proposed MAC design can considerably improve the throughput of a WLAN operating over lossy links.

In this paper, we will combine the frequency hopping (FH) and the multi-carrier code division multiple access scheme (MC-CDMA) through an internal coding. The total bandwidth will be divided to a number of sub-bands with equal bandwidth. In each signalling interval, the output of a super orthogonal encoder selects one of the sub-bands for data transmission. Sub-carriers are modulated by a user specific PN sequence, and are transmitted over the selected sub-band similar to the MC-CDMA communications. We will derive the exact bit error rate of the MC-CDMA system and the new coded system. It will be shown by analysis and simulation that the proposed system performs much better than the MC- CDMA system for the same bandwidth and spectral efficiency.