David Wake

Radio Over Fiber Link Design for Next Generation Wireless Systems

The performance of radio over fiber (RoF) links using low cost optoelectronic components is assessed for distributed antenna applications in next generation wireless systems. Important design issues are discussed and an example link design is presented for a wireless system requiring the transmission of four radio channels per link direction, each with 100 MHz bandwidth, modulation complexity of 256-QAM and 2048 OFDM subcarriers. We show that the noise introduced by the RoF links does not have a significant impact on wireless range, provided the wireless system has uplink power control. Finally, we compare the cost and performance of RoF links for this application with alternative link types that use digitized radio transmission and show that RoF is the optimum choice from a cost perspective.

Optical generation of millimeter-wave signals for fiber-radio systems using a dual-mode DFB semiconductor laser

This paper presents a new approach to the optical generation of millimeter-wave signals using a dual-mode multisection distributed feedback semiconductor laser. This simple device is capable of generating high power signals between 40 and 60 GHz with extremely high spectral purity and stability. The two optical modes produced by this laser are heterodyned on an ultrafast photodiode to give a beat signal at the mode difference frequency. The phase noise of the beat signal is greatly reduced by phase-locking the modes using an electrical drive signal applied to the laser at a subharmonic of the beat frequency. Millimeter-wave signals are obtained with a linewidth of less than 10 Hz, a phase noise of less than -85 dBc/Hz at 100 kHz offset, and a locking range of about 500 MHz. Millimeter-wave fiber-radio systems are seen as a major application area for these new compact optical sources. >

Novel techniques for high-capacity 60-GHz fiber-radio transmission systems

A broad-band 60-GHz fiber-radio transmission experiment has been performed using a combination of novel techniques. The 60-GHz carrier signal was generated using a master/slave (M/S) distributed-feedback (DFB) laser configuration, which gave high purity and high power with very wide frequency tunability. The data path was separated in the wavelength domain from the carrier path so that a remote upconversion scheme could be used to provide a fully transparent link. An electroabsorption modulator (EAM) was used as a full duplex transceiver so that bidirectional optical transmission could be implemented without the need for a laser at the remote site. Transmission of a 120-Mb/s QPSK signal over a fiber span of 13 km and a radio path of 5 m was demonstrated. Furthermore, the downstream optical signal contained the 120-Mb/s QPSK signal multiplexed with 20 channels of TV. The upstream optical signal consisted of 120-Mb/s QPSK data only. Good error performance was simultaneously achieved in both directions.

Design of low-cost multimode fiber-fed indoor wireless networks

A low-cost option for transporting global system for mobile communication, Universal Mobile Telecommunication System and wideband local area network (WLAN) signals using multimode fiber (MMF) with 850-nm vertical-cavity surface-emitting lasers (VCSELs) is investigated through range predictions from a link budget analysis. These predictions are experimentally verified for WLAN signal transmission in an office environment, using a commercial access point and a 300-m (OM1/OM2) MMF link with low-cost 850-nm VCSEL transmitters. The analysis indicates that good performance and signal coverage is possible with optimum design of indoor fiber-fed wireless systems, even when using such inexpensive components

Transmission of 60-GHz signals over 100 km of optical fiber using a dual-mode semiconductor laser source

High-purity 60-GHz signals, generated using a dual-mode DFB semiconductor laser, have been transmitted over 100 km of standard optical fiber with no observable degradation in purity. This device is shown to be a simple and compact optical source of high-purity 60-GHz signals for long-reach fiber-fed millimeter-wave radio systems.

Optically Powered Remote Units for Radio-Over-Fiber Systems

Optically powered radio-over-fiber remote units have been designed and constructed for distributed antenna system applications using separate fibers for power and signal transmission. The feasibility of this approach has been investigated through a series of transmission measurements, based on the IEEE 802.11g wireless local area networking standard at a frequency of 2.5 GHz using 64-QAM OFDM modulation at 54 Mb/s. These measurements show that high-quality multilevel signal transmission is possible with modest levels of optical power at the central unit. For example, an EVM of around 3% has been achieved for an RF output power of 0 dBm using a central unit optical power of 250 mW over a link length of 300 m.

A Comparison of Radio Over Fiber Link Types for the Support of Wideband Radio Channels

Three radio over fiber link types are compared to assess their relative performance for the optical transmission of next generation wireless signals having multiple wideband radio channels with high-level modulation. These links differ in their choice of modulation device; either a directly modulated laser (DML) or external modulation using a Mach-Zehnder modulator (MZM) or a reflective semiconductor optical amplifier (RSOA). The DML and RSOA link types are shown to suffer minimal degradation of the uplink wireless range compared to the baseline value without an optical link, using optimum components in terms of cost and performance. The optimum technology depends on the relative merits of simplicity (DML) or optical network architecture flexibility (RSOA).

Radio-Over-Fiber Access Network Architecture Based on New Optimized RSOA Devices With Large Modulation Bandwidth and High Linearity

Next-generation wireless communications systems need to have high throughputs to satisfy user demand, to be low-cost, and to have an efficient management as principal features. Using a high-performance, low-cost reflective semiconductor optical amplifier (RSOA) as a colorless remote modulator at the antenna unit, the wavelength-division multiplexing (WDM) technique can be used for supporting distributed antenna systems (DASs). Each antenna unit is connected to the central unit using optical fiber and all links are used to transmit radio signals. Due to a large optical bandwidth, RSOAs are potential candidates for cost effective WDM systems. In this paper, simulations are carried out to determine optimized RSOA devices for wireless technology. New RSOA structures are fabricated and evaluated. The optimized RSOA is electrically driven by a standard Wi-Fi input signal (IEEE 802.11 g) with a 64-quadrature amplitude modulation (QAM) format. A large modulation bandwidth and a high electrooptic gain are demonstrated, which are confirmed by good performance when using orthogonal frequency-division multiplexing techniques. Characteristics such as high linearity and large electrooptic modulation bandwidth of our RSOA are sufficient to ensure an error vector magnitude (EVM) lower than 5% with a dynamic range exceeding 35 dB in a back-to-back configuration (at 0 dBm). Uplink transmission over a 20 km of single-mode fiber is also demonstrated with EVM lower than 5% and a dynamic range exceeding 25 dB (at 5 dBm).

Radio-Over-MMF Techniques—Part I: RF to Microwave Frequency Systems

Recent work on radio-over-multimode-fiber (MMF) transmission, for the support of wireless LANs and current cellular systems operating at below 6 GHz, has shown that excellent performance (e.g., spur-free dynamic range well in excess of 100 dB.Hz2/3) can be achieved. However, it is shown here that for multisystem operation, spurious emissions may be more of a restriction than meeting good signal quality requirements (such as low error vector magnitude). Initial results are reported for error vector magnitude and adjacent channel leakage for UMTS transmission over a radio-over-MMF link with a multisystem remote antenna unit with conformance to standards being demonstrated.

Simultaneous Dual Band Transmission Over Multimode Fiber-Fed Indoor Wireless Network

Performance measurements of different combinations of digital enhanced cordless telecommunications packet radio service, global system for mobile communications, universal mobile telecommunication service, and 802.11g (54 Mbps) signals in a dual band configuration transmitted over an indoor wireless network fed by a low-cost 850-nm vertical-cavity surface-emitting laser (VCSEL)-300m multimode fiber link are presented. The feasibility of such a system is demonstrated with error vector magnitude measurements which are within the required specifications