Michael J. Crisp

Uplink and Downlink Coverage Improvements of 802.11g Signals Using a Distributed Antenna Network

A distributed antenna network (DAN) is demonstrated to improve the coverage of in-building wireless services. A doubling in the number of locations with a high throughput is achieved. A detailed analysis of the performance improvement of a three-antenna DAN over a single-antenna system shows that 10-dB more power would be required from the single antenna to achieve a comparable performance. The effect of the additional delay spread generated by the DAN is also discussed, and the conditions under which it does not degrade performance are investigated.

Demonstration of a Radio over Fibre Distributed Antenna Network for Combined In-building WLAN and 3G Coverage

A RF-over-fibre distributed multi-antenna network is demonstrated to improve coverage and reduce the required dynamic range of co-existing IEEE 802.11 g WLAN and 3G services by using overlapping cells, fed from a single signal source.

Wideband Radio over Fiber Distributed Antenna Systems for Energy Efficient In-Building Wireless Communications

The power consumption of radio over fiber fed distributed antenna networks is modeled. By optimization of the antenna unit RF output power, the power consumption is minimized. Optimized broadband multi-service and narrowband single service solutions are compared and it is shown that when more than 2 services are to be provided, the broadband multi-service system is more efficient.

Feasibility Demonstration of a Mode-Division Multiplexed MIMO-Enabled Radio-Over-Fiber Distributed Antenna System

In this paper the feasibility of mode-division multiplexing (MDM) for implementing multiple-input multiple-output (MIMO) radio-over-fiber (RoF) distributed antenna systems (DAS) is experimentally demonstrated, where the MIMO algorithm is able to reconstruct the data signals by overcoming distortion and crosstalk in both the free-space RF and optical fiber channels. This is achieved through RF characterization of an MDM RoF link, which is experimentally demonstrated to be capable of supporting at least 4 × 4 MIMO with 6 GHz channels over long lengths of MMF (2 km compared to ~300 m typically found in MMF-based RoF DASs) and under tight fiber bending conditions (bend radius as low as 7.6 mm), which are commonly encountered in in-building fiber installations. First, experimental RF measurements are performed over a 2 km section of OM2 fiber, mode-multiplexed using a spatial light modulator (SLM) based MUX/DEMUX system, and it is shown to offer an RF condition number of <;14 dB for up to 4 × 4 MIMO with 6 GHz channels, sufficient to enable good performance for⊣ most modern wireless protocols. Next, the effect of fiber curvature on RF performance is experimentally analysed using a 10 m section of OM3 fiber. It is seen that with a bend radius as low as 7.2 mm, a condition number of ~10 dB can be achieved for up to a 6 × 6 MIMO system with 6 GHz channels. Although an SLM-based MUX/DEMUX is used here, condition number is not dependent on the exact mode-launching system used provided that orthogonal combinations of modes are excited, which is true of most MDM systems. It is therefore concluded that the RF characterization presented here demonstrates by proof-of-principle the feasibility of graded-index) MMF to support at least 4 × 4 MIMO with broadband channels via MDM over lengths up to 2 km and with fiber bend radii as low as 7.2 mm.

Demonstration of improved passive UHF RFID coverage using optically-fed distributed multi-antenna system

Optically-fed distributed antenna system (DAS) technology is combined with passive ultra high frequency (UHF) radio frequency identification (RFID). It is shown that RFID signals can be carried on directly modulated radio over fiber links without impacting their performance. It is also shown that a multi-antenna DAS can greatly reduce the number of nulls experienced by RFID in a complex radio environment, increasing the likelihood of successful tag detection. Consequently, optimization of the DAS reduces nulls further. We demonstrate RFID tag reading using a three antenna DAS system over a 20m×6m area, limited by building constraints, where 100% of the test points can be successfully read. The detected signal strength from the tag is also observed to increase by an average of approximately 10dB compared with a conventional switched multi-antenna RFID system. This improvement is achieved at +31dBm equivalent isotropically radiated power (EIRP) from all three antenna units (AUs).

Performance Analysis of Passive UHF RFID Systems Under Cascaded Fading Channels and Interference Effects

In this paper, the performance of monostatic and bistatic passive ultra high frequency radio frequency identification (UHF RFID) systems under the effects of cascaded fading channels and interference is studied. The performance metric used is tag detection probability defined as the probability that the instantaneous received power is higher than the readers sensitivity. A closed-form expression of the detection probability is derived using cascaded forward and backscatter fading channels and the reader antennas orientation relative to the tag. Furthermore, the performance of passive UHF RFID systems under reader-to-tag interference caused by both the desired RFID signal and multiple RFID interferers is analyzed, and the effect of constructive and destructive interferences is examined. In addition, the maximum reading range in ideal, multipath fading, and interfering environments is presented. To the best of our knowledge, this is the first work that provides a 3-D performance analysis of the passive UHF RFID systems under cascaded fading channels. The obtained results are very useful for the design and optimization of passive UHF RFID systems from an RF physical channel point of view.

High-Order Distortion in Directly Modulated Semiconductor Lasers in High-Loss Analog Optical Links With Large RF Dynamic Range

A theoretical and experimental investigation of the effects of high-order nonlinear distortion products produced by directly modulated semiconductor lasers on the performance of high-loss analog optical communication links requiring large RF dynamic range is reported. In order to provide sufficient RF dynamic range to support radio services in links with high optical transmission loss, for example in radio over free-space optics (RoFSO), while keeping costs low, it is necessary to use directly modulated lasers. However, in these applications the lasers must be driven to high modulation depths to maximize dynamic range. Simulations show that under these unique conditions the first detectable nonlinear distortion is often the result of dynamic distortion due to the laser being driven near threshold. It is shown that this type of distortion is characterized by a sharp increase in the contribution of high-order (fourth order or greater) nonlinear terms resulting from the influence of laser relaxation oscillations. As a consequence, the third-order spurious-free dynamic range (SFDR) metric no longer accurately reflects the performance of such links as it assumes that third order effects are dominant. An alternative measure of dynamic range called dynamic-distortion-free dynamic range (DDFDR) is proposed. This differs in that the upper limit is defined as the modulating power at which the peak optical modulation index (OMI) reaches unity. At this point the error vector magnitude (EVM) measured for a range of different wireless services starts to increase rapidly due to high order distortion. This makes DDFDR a practical, service-independent metric of dynamic range. For two different wireless services it is observed experimentally that on average the DDFDR upper limit predicts the EVM knee point to within 1.1 dB, while the third-order SFDR predicts it to within 6.2 dB. The DDFDR is thus shown to be a more accurate indicator of real link performance when high-order distortion is dominant.

Wide Area Passive UHF RFID System Using Antenna Diversity Combined With Phase and Frequency Hopping

This paper presents a long range and effectively error-free ultra high frequency (UHF) radio frequency identification (RFID) interrogation system. The system is based on a novel technique whereby two or more spatially separated transmit and receive antennas are used to enable greatly enhanced tag detection performance over longer distances using antenna diversity combined with frequency and phase hopping. The novel technique is first theoretically modelled using a Rician fading channel. It is shown that conventional RFID systems suffer from multi-path fading resulting in nulls in radio environments. We, for the first time, demonstrate that the nulls can be moved around by varying the phase and frequency of the interrogation signals in a multi-antenna system. As a result, much enhanced coverage can be achieved. A prototype RFID system is built based on an Impinj R2000 transceiver. The demonstrator system shows that the new approach improves the tag detection accuracy from to 100% over a 20 m ×15 m area, compared with a conventional switched multi-antenna RFID system.

Experimental Evaluation of Layout Designs for 3

This paper experimentally demonstrates that, for two representative indoor distributed antenna system (DAS) scenarios, existing radio-over-fiber (RoF) DAS installations can enhance the capacity advantages of broadband 3 × 3 multiple-input-multiple-output (MIMO) radio services without requiring additional fibers or multiplexing schemes. This is true for both single- and multiple-user cases with a single base station and multiple base stations. First, a theoretical example is used to illustrate that there is a negligible improvement in signal-to-noise ratio (SNR) when using a MIMO DAS with all N spatial streams replicated at N RAUs, compared with a MIMO DAS with only one of the N streams replicated at each RAU for N ≤ 4. It is then experimentally confirmed that a 3 × 3 MIMO DAS offers improved capacity and throughput compared with a 3 × 3 MIMO collocated antenna system (CAS) for the single-user case in two typical indoor DAS scenarios, i.e., one with significant line-of-sight (LOS) propagation and the other with entirely non-line-of-sight (NLOS) propagation. The improvement in capacity is 3.2% and 4.1%, respectively. Then, experimental channel measurements confirm that there is a negligible capacity increase in the 3 × 3 configuration with three spatial streams per antenna unit over the 3 × 3 configuration with a single spatial stream per antenna unit. The former layout is observed to provide an increase of ~ 1% in the median channel capacity in both the single- and multiple-user scenarios. With 20 users and three base stations, a MIMO DAS using the latter layout offers median aggregate capacities of 259 and 233 bit/s/Hz for the LOS and NLOS scenarios, respectively. It is concluded that DAS installations can further enhance the capacity offered to multiple users by multiple 3 × 3 MIMO-enabled base stations. Further, designing future DAS systems to support broadband 3 × 3 MIMO systems may not require significant upgrades to existing installations for small numbers of spatial streams.

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A wideband-multiservice RoF DAS with sensing and communications functionality is demonstrated, using an electronic feedforward second-harmonic cancellation scheme to reduce spurious emissions from high power RFID signals.