Phase-based Ranging in Narrowband Systems with Missing/Interfered Tones

The growth in the number of low-cost narrow band radios such as Bluetooth low energy (BLE) enabled applications such as asset tracking, human behavior monitoring, and keyless entry. The accurate range estimation is a must in such applications. Phase-based ranging has recently gained momentum due to its high accuracy in multipath environment compared to traditional schemes such as ranging based on received signal strength. The phase-based ranging requires tone exchange on multiple frequencies on a uniformly sampled frequency grid. Such tone exchange may not be possible due to some missing tones, e.g., reserved advertisement channels. Furthermore, the IQ values at a given tone may be distorted by interference. In this paper, we proposed two phase-based ranging schemes which deal with the missing/interfered tones. We compare the performance and complexity of the proposed schemes using simulations, complexity analysis, and two measurement setups. In particular, we show that for small number of missing/interfered tones, the proposed system based on employing a trained neural network (NN) performs very close to a reference ranging system where there is no missing/interference tones. Interestingly, this high performance is at the cost of negligible additional computational complexity and up to 60.5 Kbytes of additional required memory compared to the reference system, making it an attractive solution for ranging using hardware-limited radios such as BLE

An improved dropping algorithm for line-of-sight massive MIMO with max-min power control

In line-of-sight massive MIMO, there is a nonnegligible probability that two users become highly correlated, which leads to a reduction in the achievable sum-rates of linear precoders. In this letter, threshold values of a previously proposed dropping algorithm are found analytically to avoid repeating a large number of simulations to find the optimal threshold. These thresholds allow us to improve conjugate beamforming (CB) and zero-forcing (ZF) sum-rates with max-min power control. By using the proposed threshold values, the CB and ZF sum-rates are maximized, when there are only two correlated users. In addition, by using the derived thresholds, a modified dropping algorithm is proposed for channels with any number of correlated users. The results of the simulation scenarios show that at signal to noise ratio of 20 dB and 120 antennas at the base station, the modified algorithm improves the average CB and ZF sum-rates up to 36% and 5%, respectively

An improved dropping algorithm for line-of-sight massive MIMO with Tomlinson–Harashima precoding

One of the problems in line-of-sight massive MIMO is that a few users can have correlated channel vectors. To alleviate this problem, a dropping algorithm has been proposed in the literature, which drops some of the correlated users to make the spatial correlation among the remaining users be less than a certain threshold. Thresholds were found by running a large number of simulations. In this letter, the same dropping algorithm is analyzed for a known nonlinear precoder: Tomlinson-Harashima precoder. Instead of simulation-based thresholds, closed-form analytical expressions are derived in this letter for two power allocation schemes: max-min and equal received power control schemes. It is shown that the derived thresholds are optimal in terms of achievable sum-rate when there is only one correlated pair of users. For channels with multiple pairs of correlated users, simulation results show that using the derived thresholds improves the 5th percentile sum-rate. Due to the fairness criterion of max-min, the improvement for max-min power control is much higher than equal received power control

A Low-Complexity Hybrid Linear and Nonlinear Precoder for Line-Of-Sight Massive MIMO with Max-Min Power Control

In line-of-sight (LOS) massive MIMO, there is a nonnegligible probability that the channel vectors of some users become correlated. In these correlated scenarios, nonlinear precoders can be used instead of linear precoders at the cost of high computational complexity. To reduce the complexity of nonlinear precoders, hybrid linear and nonlinear precoders have been suggested in 5G New Radio (NR). In this paper, we find the probability that there is at least one pair of correlated users and we find the average number of correlated users. We propose a hybrid linear and nonlinear precoder (HLNP) with max-min power control for which the served users are divided into two groups. By employing a proposed modified Tomlinson-Harashima Precoding (THP), we design and combine the transmit vectors of the two groups such that inter-group interference is removed. Simulation results show that by employing HLNP instead of zero-forcing, the required transmit power to assure a given average block error rate (BLER) with 95% probability is reduced. For a 64-antennas BS, when modified THP is used for 3 out of 10 users in HLNP, the transmit power is reduced by up to 4.70 dB to assure an average BLER of 10-2 using 16QAM and 64QAM constellations with NR low-density parity-check codes

MIMO performance evaluation of isotropic, directional and highly-directional antenna systems for mm-wave communications

In this paper, we investigate how directional and highly-directional antenna systems using fixed beams can be beneficial in terms of aggregated channel and antenna gains, channel correlation and the massive multiple-input multiple-output (MIMO) capacity in both line-of-sight (LOS) and non-LOS (NLOS) scenarios for single user MIMO (SU-MIMO). It is shown that narrower beams have stronger aggregated channel and antenna gain. However, narrow beamwidth triggers a higher channel correlation as fewer scatterers are seen. A possible solution to reduce the correlation among the beams is to properly decorrelate the beams in advance. To this end, we partition the area of interest and devote one specific partition to each beam to minimize the possible overlaps among the beams. Simulation results show that fixed beam SU-MIMO systems using such highly-directional beams can provide higher MIMO capacity in comparison to isotropic and directional antenna systems

DropNet: An Improved Dropping Algorithm Based On Neural Networks for Line-of-Sight Massive MIMO

In line-of-sight massive MIMO, the downlink channel vectors of few users may become highly correlated. This high correlation limits the sum-rates of systems employing linear precoders. To constrain the reduction of the sum-rate, few users can be dropped and served in the next coherence intervals. The optimal strategy for selecting the dropped users can be obtained by an exhaustive search at the cost of high computational complexity. To alleviate the computational complexity of the exhaustive search, a correlation-based dropping algorithm (CDA) is conventionally used, incurring a sum-rate loss with respect to the optimal scheme. In this paper, we propose a dropping algorithm based on neural networks (DropNet) to find the set of dropped users. We use appropriate input features required for the user dropping problem to limit the complexity of DropNet. DropNet is evaluated using two known linear precoders: conjugate beamforming (CB) and zero-forcing (ZF). Simulation results show that DropNet provides a trade-off between complexity and sum-rate performance. In particular, for a 64-antenna base station and 10 single-antenna users: (i) DropNet reduces the computational complexity of the exhaustive search by a factor of 46 and 3 for CB and ZF, respectively, (ii) DropNet improves the 5th percentile sum-rate of CDA by 0:86 and 2:33 bits/s/Hz for CB and ZF, respectively

Uniform Linear Arrays With Optimized Inter-Element Spacing for LOS Massive MIMO

In this letter, a uniform linear array (ULA) is proposed for line-of-sight massive multiple-input-multiple-output (MIMO). It is assumed that the number of antennas is fixed. For a given ULA with an arbitrary inter-element spacing, the probability that the correlation among the channel vectors of two users being above a threshold value is derived. The inter-element spacing of the proposed ULA is the one for which the aforementioned probability is minimized. To show the effectiveness of the proposed ULA, simulation results for two scenarios are given for a 64-antenna ULA that serves 6 single-antenna users. By using the proposed ULA instead of conventional half-wavelength ULA, 5th percentile sum-rate for zero-forcing precoder is improved by 9.90 bits/channel use in first scenario without dropping, and by 1.43 bits/channel use in second scenario with dropping 1 user

Effect of Antenna Array Element Separation on Capacity of MIMO Systems Including Mutual Coupling

status: Published onlin

A Low-Power 6-to-9GHz IEEE 802.15.4a/4z Compliant IR-UWB Transceiver with Pulse Pre-Emphasis Achieving High ToA Precision

This work presents an IEEE 802.15.4a/4z compliant IR-UWB transceiver for high-precision ranging. By virtue of the proposed digital deserialization-serialization, the TX can generate the Inter-Symbol-Interference (ISI) free IEEE 802.15.4a/4z packet. The proposed analog Finite Impulse Response (FIR)-based TX pre-emphasis improves 3.5× Time of Arrival (ToA) measurement precision without substantial power overhead and fulfills the spectrum requirement of the standard and the worldwide UWB regulations. The presented transceiver consumes 8.7 mW in TX mode and 21 mW in RX mode. IEEEFALS