The fast growth of drone applications in industrial, commercial and consumer domains in recent years has caused great security, safety and privacy concerns. For this reason, a demand for solutions of drone detection and monitoring in consumer market can be foreseen in the near future. For detecting drones that employ Zadoff-Chu (ZC) sequences for synchronization, these ZC sequences can be used to determine their presence in the air. However, it is a great challenge to blindly detect thousands of unknown ZC sequences possibly used by the drones in real time. Existing solutions mainly developed for LTE systems cannot be directly applied to the blind detection of ZCs in drones without incurring huge cost. In this paper, a low-complexity cost effective blind ZC detection method based on double differential is proposed for low-cost drone detection and monitoring systems. Signal-to-noise ratio (SNR) lower bounds are analytically derived for low and high SNR regimes. Monte Carlo simulations show the proposed scheme performs well in moderate and high SNR.

In this paper we study the beamforming vector quantization and feedback transmission problem for a cooperative transmission environment. Feedback is the primary means of providing the transmitter with channel state information (CSI) in a frequency division duplex (FDD) system. The conventional codebook approach uses a common codebook at the transmitter and at the receiver, while the feedback takes the form of the index of the codebook. This approach has a complexity that scales exponentially with the number of transmit antennas M, making the approach less favorable when M is large. We propose to use trellis-based quantization to reduce the complexity to grow linearly in M. A codebook design criteria is derived for the trellis-based quantizer. We also present three enhancements to the base scheme, each giving 0.2-0.8 dB gain. These enhancements address issues relevant to feedback error, trellis termination, and unequal path-loss from different transmission points. Performance results are shown in numerical simulations.

Trellis-based quantization is a suitable method for reporting channel state information in multi base-station or base-station-relay coordinated transmission schemes. Due to different path loss and shadowing from each transmitting station, the receiver experiences different long-term average signal powers from each transmitter. We first propose to use a tail-biting trellis to improve the performance of the vector quantization proposed in. To reduce decoding complexity, we present a trellis labeling technique where efficient encoding and decoding can be performed by traversing the trellis twice. Lastly, we introduce a mechanism for dynamically allocating quantization bits amongst different parts of the augmented channel state vector. A trellis simplification procedure that keeps the number of trellis states at each stage to four is shown to provide a satisfactory performance.

We propose an intercell downlink orthogonal frequency division multiple access (OFDMA) scheduling technique in a sectorized cellular network. Adjacent sectors from neighboring cells form a cluster and each OFDMA resource block is allocated to the rate-maximizing sector. Compared to a cellular network that uses conventional fractional frequency reuse (FFR) technique, our proposed system requires only slightly more backhaul traffic while providing an appreciable performance gain. Intercell scheduling, which grants a resource exclusively to the rate-maximizing cell within a cluster, is a simple and powerful base station cooperation technique that balances non-cooperation and full cooperation. We find out that a tri-sectored network is particularly well-suited to applying inter-sector scheduling as each cluster is relatively isolated from other clusters. We provide an option to adjust the load on backhaul traffic by adjusting the granularity of the OFDMA resource under contention. We also provide an option to optimally swap resources. Analysis on performance gain for a few configurations are given. Simulations are provided to verify and illustrate the claimed performance gain.

Generally limited feedback systems that multiplex multiple user signals are noise power limited in the low signal-tonoise- ratio (SNR) regime and interference power limited in the high SNR regime. If the amount of feedback does not grow with SNR, then there is a sum rate ceiling that increasing the transmit power alone cannot surpass. This paper proposes a simple dual mode system where the base station serves either one user or as many users as the number of transmit antennas. The switching mechanism is smooth and is based on instantaneous system conditions. The mobile determines its preferred transmission mode by using a very simple signal-to-interference-and-noiseratio (SINR) threshold. Based on the mobiles' feedback, the base station chooses the method of signalling accordingly. With a finite number of feedback bits per mobile, it is shown that the proposed system achieves close to the maximum of the sum-rate for single user and multiuser modes. We identify the preferrable mode for an asymptotically large number of users and/or SNR. This proposed architecture is suitable for systems with moderate coherence time, a moderate to large number of users, and a moderate SNR that cannot afford complex processing at the base station or at the mobile.

In a two-way system where two users transmit data to each other, limited feedback beamforming is a simple method to supply channel state information to the transmitter (CSIT) for a multiple-input-multiple-output (MIMO) system when channel reciprocity is unavailable. For analytical tractability, most existing papers assume the existence of an ideal fixed-rate feedback channel to assist the transmitter to adapt to instantaneous channel conditions. The relationship between the feedback rate and data rate is typically analyzed in a unidirectional manner. In reality, judicious resource allocation to transmitting feedback and data leads to a tradeoff between the effective forward and reverse data rates. In this paper, we represent the achievable rate by effective SNRs, and we present a framework to analyze the tradeoff. We find that the forward and reverse rate tradeoff can be decomposed into two local tradeoffs, resulting from the resource allocation policy of each user. The local tradeoff region for each user is found in closed-form, whereas the overall tradeoff region is approximated for the special case when the two users have equal hardware configurations.

Limited feedback systems that simultaneously transmit to multiple users are noise power limited at low SNR and interference power limited at high SNR. Specifically, there is a sum rate upper bound such that increasing the transmit power alone cannot surpass. In this paper, we propose a dual-mode system that selects between single user mode and multiuser mode. The mobile determines its preferred transmission mode by a simple threshold rule of its SINR. Judiciously combining mobiles' feedback, the base station with MTtransmit antennas chooses the better communication mode. It is shown that this proposed system asymptotically achieves unbounded capacity growth when increasing the number of mobiles or when increasing the SNR, without requiring extra feedback bits. We show the asymptotically preferable mode as the number of users and/or SNR increases. Lastly, we use computer simulations to verify our findings.

In multiple antenna wireless systems, beamforming is a simple technique for guarding against the negative effects of fading. Unfortunately, beamforming requires the transmitter to have knowledge of the forward-link channel which is often not available a priori. One way of overcoming this problem is to design the beamforming vector using a limited number of feedback bits sent from the receiver to the transmitter. In limited feedback beamforming, the beamforming vector is restricted to lie in a codebook that is known to both the transmitter and receiver. Random vector quantization (RVQ) is a simple approach to codebook design that generates the vectors independently from a uniform distribution on the complex unit sphere. This correspondence presents performance analysis results for RVQ limited feedback beamforming