Photonics-enabled sub-Nyquist radio frequency sensing based on temporal channelization and compressive sensing

A novel approach to sensing broadband radio frequency (RF) spectrum beyond the Nyquist limit based on photonic temporal channelization and compressive sensing is proposed. A spectrally-sparse RF signal with unknown frequencies is modulated onto a highly chirped optical pulse. An optical channelizer slices the modulated pulse spectrum, which is equivalent to temporally sampling the RF waveform thanks to the dispersion-induced wavelength-to-time mapping. This serial-to-parallel conversion avoids the use of a high-speed detector and digitizer. Furthermore, compressive sensing with optical random demodulation is achieved using a spatial light modulator, enabling the system to capture the wideband multi-tone RF signal with a sampling rate far lower than the Nyquist rate. It is demonstrated that the temporal channelization system with a channel spacing of 20 GHz achieves RF spectrum sensing with a high resolution of 196 MHz. With an equivalent sampling rate of only 25 GHz, a 50-GHz broadband two-tone RF signal can be captured and reconstructed by the system thanks to compressive sensing with a compression ratio of 4

Protocol parameter selection for fiber-supported IEEE 802.16m networks

In this paper we investigate protocol issues that might arise due to the extra fiber propagation delay in fiber-fed IEEE 802.16m networks. Our study indicates that although the fiber delay might affect network performance, an informed choice of protocol parameters, such as the guard times and the ranging channel structure, can minimize the reduction in efficiency and allow for relaxation of some of the constraints imposed on the optical distribution network architecture

Fiber link design considerations for cloud-Radio Access Networks

Analog radio over fiber (RoF) links may offer advantages for cloud-Radio Access Networks in terms of component cost, but the behavior of the distortion with large numbers of subcarriers needs to be understood. In this paper, this is presented in terms of the variation between subcarriers. Memory polynomial predistortion is also shown to compensate for RoF and wireless path distortion. Whether for digitized or analog links, it is shown that appropriate framing structure parameters must be used to assure performance, especially of time-division duplex systems

Nonlinearity and Noise Effects in Multi-level Signal Millimeter-Wave over Fiber Transmission using Single- and Dual-Wavelength Modulation

We transmit multilevel quadrature amplitude modulation (QAM) data-IEEE 802.16 schemes-at 20 MSps and an orthogonal frequency-division multiplexing (OFDM) 802.11 g signal (54 Mbps) with a 25 GHz millimeter-wave over fiber system, which employs a dual wavelength source, over 20 km of single mode fiber. Downlink data transmission is successfully demonstrated over both optical and wireless (up to 12 m) paths with good error vector magnitude. An analysis of two different schemes, in which data is applied to one (single) and both (dual) of the wavelengths of a dual wavelength source, is carried out. The system performance is analyzed through simulation and a good match with experimental results is obtained. The analysis investigates the impact of Mach-Zehnder modulator (MZM) and RF amplifier nonlinearity and various noise sources, such as laser relative intensity noise, amplified spontaneous emission, thermal, and shot noise. A comparison of single carrier QAM IEEE 802.16 and OFDM in terms of their sensitivity to the distortions from MZM and RF amplifier nonlinearity is also presented

Capacity and Error Performance Verification of Multi-Antenna Schemes in Radio-over-Fiber Distributed Antenna System

A radio-over-fiber distributed antenna system permits larger physical separation between antennas in a wireless system’s infrastructure; this investigation verifies that improved performance – lower error rates and higher capacities – can thus be achieved. In this paper, specific single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) algorithms are compared in an experimental radio over fiber system, using user-defined processing functions for the signals. It is shown that significantly reduced symbol error rate (SER) and modestly increased capacity is achieved for a wireless 1x2 SIMO uplink using the maximal ratio combining (MRC) processing algorithm and 2x1 MISO downlink using the Alamouti space time block coding (STBC) scheme. Further, SER is reduced for a downlink 2x2 wireless MIMO using the zero-forcing algorithm while, most importantly, greatly increased capacity is achieved through the spatial multiplexing gain

Fronthaul evolution: From CPRI to Ethernet

It is proposed that using Ethernet in the fronthaul, between base station baseband unit (BBU) pools and remote radio heads (RRHs), can bring a number of advantages, from use of lower-cost equipment, shared use of infrastructure with fixed access networks, to obtaining statistical multiplexing and optimised performance through probe-based monitoring and software-defined networking. However, a number of challenges exist: ultra-high-bit-rate requirements from the transport of increased bandwidth radio streams for multiple antennas in future mobile networks, and low latency and jitter to meet delay requirements and the demands of joint processing. A new fronthaul functional division is proposed which can alleviate the most demanding bit-rate requirements by transport of baseband signals instead of sampled radio waveforms, and enable statistical multiplexing gains. Delay and synchronisation issues remain to be solved

Energy-Efficient Localization-based Link Setup Scheme for Device-to-Device Communications

A new energy efficient link setup scheme for device-to-device (D2D) communications in cellular networks is proposed that employs approximate localization easily performed using new radio technologies. To set up a D2D link, the obtained location estimates are used to judge whether two user-devices can be a D2D pair, and to control the transmit power between two devices, taking into account the accuracy of the estimated distance between them. Simulation results show that the scheme not only removes the neighbor discovery step, leading to faster setup, but also significantly improves energy efficiency and resource block utilization, while maintaining a high success probability for the D2D discovery and communication setup

Improved IEEE 802.11 point coordination function considering fiber-delay difference in distributed antenna systems

In this paper, we present an improved IEEE 802.11 wireless local-area network (WLAN) medium access control (MAC) mechanism for simulcast radio-over-fiber-based distributed antenna systems where multiple remote antenna units (RAUs) are connected to one access point (AP). In the improved mechanism, the fiber delay between RAUs and central unit is taken into account in a modification to the conventional point coordination function (PCF) that achieves coordination by a centralized algorithm. Simulation results show that the improved PCF outperforms the distributed coordination function (DCF) in both the basic-access and request/clear-to-send modes in terms of the total throughput and the fairness among RAU

Experimental analysis of single and multiple antenna units in uplink of radio-over-fiber distributed antenna system

Increasing the number of antennas either at the transmitter or receiver has been shown to improve system reliability without occupying additional spectrum. In this paper, we experimentally investigate the error vector magnitude (EVM) of single and multiple remote antenna units (RAU) focusing on uplink transmission. We demonstrate that for 64-QAM modulation, the EVM requirement of 6.5% could be achieved with multiple separated RAUs in situations where a single RAU fails to meet this requirement. The EVM result was obtained as the transmitting device was placed at different locations in a typical office environment with OFDM signals gathered through the RAUs and brought back to a central unit for processing. The EVM results show that using multiple RAUs and an efficient signal combining technique, here, maximal ratio combining (MRC), the EVM performance could reduce by approximately 2% when the distance between the RAUs was 0.3m and further reduced by 4% and 6% when the inter-RAU distance was 2m and 4m, respectively, compared to a single RAU