This paper presents a novel multiple-access modulation scheme which combines key characteristics of single carrier frequency division multiple access (SC-FDMA) with continuous phase modulation (CPM) in order to generate a power efficient waveform. CPM-SC-FDMA is developed based upon the observation that the samples from a CPM waveform may be treated as "data symbols" taken from a constant-envelope encoder. As with any encoder output, these samples may be precoded using the Discrete Fourier Transform and transmitted using SC-FDMA. Having originated from a constant envelope CPM waveform, CPM-SC-FDMA can potentially retain much of the power efficiency of CPM-thus resulting in a lower peak-to-average power ratio (PAPR) than conventional SC-FDMA. In this paper, we account for the information rate, memory, power efficiency, bit error rate (BER) performance and spectral occupancy of CPM-SC-FDMA. In addition, we investigate the impact of amplifier nonlinearity on BER performance as the number of users increases. Finally, we provide a detailed numerical comparison with a commensurate convolutionally coded QPSK-SC-FDMA scheme (CC-QPSK-SC-FDMA). We show a CPM-SC-FDMA scheme that provides an overall gain of up to 4 dB relative to the CC-QPSK-SC-FDMA scheme over a frequency-selective channel.

This article presents a summary of 3GPP Long Term Evolution (LTE) radio system performance during the execution of a multi-site field trial. This exhaustive testing campaign, performed over the lower 700 MHz and 2 GHz bands, includes a battery of stationary and mobility throughput cases, multi-user capacity scenarios, handover performance and latency tests, that have been designed to reveal LTE radio performance under a variety of realistic user scenarios. Tests have been performed using a Category 2 LTE UE, which can handle a maximum transport of 50 Mbps in the downlink and 25 Mbps in the uplink. As the results indicate, the system boasts a peak downlink single-user throughput in excess of 49 Mbps and a peak uplink single-user throughput observed of 19 Mbps, which is quite close to the theoretical uplink limit of 21 Mbps. In multi-user scenarios with four active users, in the best case, we have measured a cell throughput of 47 Mbps in the downlink and 20 Mbps in the uplink, which is close to the theoretical best. Finally, as we show, the system achieves a handover success rate of 100% and a best case average user plane latency of 22ms.

In this paper, we investigate the power efficiency and bit error rate performance of two spectrally efficient CPM-SCFDMA (Continuous Phase Modulated Single Carrier Frequency Division Multiple Access) waveforms. CPM-SC-FDMA is derived by sampling a Continuous Phase Modulated (CPM) waveform and then DFT-precoding the resulting signal samples for transmission using SC-FDMA. Having originated from a constant envelope CPM waveform, CPM-SC-FDMA can potentially retain much of the power efficiency of CPM-thus resulting in a lower peak-to-average power ratio than conventional SC-FDMA. As we show in this paper, when taking the difference in power amplifier backoff requirements into account, CPM-SC-FDMA can provide an overall gain of up to 4 dB relative to convolutionally encoded QPSK-SC-FDMA over a frequency-selective channel.

Multicarrier orthogonal frequency division multiplexing (OFDM) supports high data rate wireless communication using orthogonal frequency channel transmissions and offers excellent immunity against fading and intersymbol interference. However, it is characterized by a high peak-to-average power ratio (PAPR), which presents a major challenge for battery- driven terminals requiring efficient power amplification. Single carrier FDMA (SC-FDMA) is a variant of OFDM in which the data symbols are modulated in the time domain, which results in a more power efficient scheme. Continuous phase modulation (CPM) forms a class of single carrier constant amplitude waveforms which are known to be power efficient since the PAPR is always 0 dB. In this paper, we present a novel CPM-SC-FDMA modulation scheme which combines key characteristics of SC-FDMA and CPM to produce a constant envelope waveform which is transmitted over a set of OFDM subcarriers. Thus, this new scheme embodies the power efficiency of single-carrier CPM and the low implementation complexity of SC-FDMA. The basis of our approach is found in the observation that the discrete-time samples from the CPM waveform constitute a set of constant envelope time domain "symbols." When used with an interleaved FDMA (IFDMA) subcarrier mapping, the resulting waveform retains the constant envelope property of CPM. Simulations in AWGN and frequency selective channels indicate that by careful selection of the CPM- SC-FDMA parameters, that the bit error rate performance can improve upon that of conventional SC-FDMA.

We compare low-complexity schemes for soft-output detection of continuous phase modulations (CPMs). In particular, we address the problem of minimizing the complexity of the front end filters and that of the trellis exploited by the detection algorithm, with the aim of assuring a negligible performance degradation with respect to the optimal full-complexity receiver. We show that the approach providing the simplest front end is that based on the CPM decomposition proposed by Moqvist and Aulin. On the other hand, we prove that the most convenient solution in terms of trellis complexity is provided by the CPM decomposition proposed by Mengali and Morelli, possibly combined with suitable techniques for reduced trellis search.

This paper investigates the problem of resource allocation and scheduling for an orthogonal frequency division multiple access (OFDMA) broadband wireless network. We formulate a utility-based cross-layer resource management framework that exploits instantaneous channel state information at the base station in order to schedule traffic during each frame. During each decision epoch, the objective is to find an efficient and fair rate and sub-carrier allocation policy that maximizes the average network utility subject to certain constraints. We develop an equivalent graph theoretical model for the cross-layer assignment problem and show its equivalence to the classical problem of finding the Maximum Weight Matching (MWM) on a bipartite graph. This is a well-studied problem in classical graph theory and several well-known solutions exist. For the optimal assignment, we consider the Hungarian algorithm - which always achieves the maximal network utility — and compare its performance to a sub-optimal modified min-sum belief propagation algorithm. Through simulations, we demonstrate the negligible difference in performance between the two.

Cooperative relay networks have been shown to improve performance in wireless communication systems as a form of spatial diversity. In this paper, we investigate the error rate performance in a single path relay network and a multiple path relay network using orthogonal frequency division multiplexing (OFDM) signals. Using the amplify-and-forward and decode-and-forward relay algorithms, we derive input-output relations for the two networks. For the amplify-and-forward case, we consider two relay power allocation schemes. The first is constant gain allocation, where the amplifying gain is constant for all subcarriers. The second is equal power allocation, where each subcarrier transmits the same power. The former scheme does not require channel state information (CSI), while the latter one does. For the decode-and-forward case, the transmitter and each relay are assumed to have uniform power allocations. We simulate the word error rate (WER) performance for the two networks. For the single path relay network, amplify-and-forward gives very poor performance, because as we increase the distance between the transmitter and receiver (and thus, add more relays), more noise and channel distortion enter the system. Decode- and-forward gives significantly better performance because noise and channel distortion are eliminated at each relay. For the multiple path relay network, decode-and-forward again gives better performance than amplify-and-forward. However, the performance gains are small compared to the single path relay network case. Therefore, amplify-and-forward may be a more attractive choice in this case due to its lower complexity.

The Laurent decomposition expresses any binary single-h CPM waveform as the summation of a finite number of pulse amplitude modulated components, and this result has been useful in the development of a class of reduced complexity CPM detection schemes. In a recent generalization, it has been shown that a similar finite-term amplitude modulation expansion exists for all variants of CPM, regardless of signal complexity, with the important distinction that the amplitude modulated pulses are, generally, data-dependent. Furthermore, it has been shown that most of the signal power is typically concentrated in the first 1-2 principle components of the expansion, which suggests a possible reduction in receiver complexity viz. the optimal maximum likelihood sequence detector. In this paper, we investigate the bit error rate (BER) performance of a maximum likelihood sequence detector when the incoming signal is matched to the data-dependent pulse modulation components found in this new signal representation. Numerical results suggest that there is a negligible decrease in performance between the optimal conventional matched filter receiver and a reduced complexity, sub-optimal scheme that only uses the first 1-2 (principle) signal components in the construction of the matched filter bank.

This paper investigates the problem of resource allocation and scheduling for an orthogonal frequency division multiple access (OFDMA) broadband wireless network We formulate a utility-based cross-layer resource management framework that exploits instantaneous channel state information at the base station in order to schedule traffic during each frame. During each decision epoch, the objective is to find an efficient and fair rate and sub-carrier allocation policy that maximizes the average network utility subject to certain constraints. We develop an equivalent graph theoretical model for the cross-layer assignment problem and show its equivalence to the classical problem of finding the maximum weight matching (MWM) on a bipartite graph. This is a well-studied problem in classical graph theory and several well-known solutions exist. For the optimal assignment, we consider the Hungarian algorithm - which always achieves the maximal network utility - and compare its performance to a sub-optimal modified min-sum belief propagation algorithm. Through simulations, we demonstrate the negligible difference in performance between the two.

The Laurent Decomposition expresses anybinarysingle-hcontinuous phase modulated (CPM) signal as the summation of a finite number of pulse amplitude modulated (PAM) waveforms, and the resulting signal space is so constructed that the waveform can usually be synthesized with a reasonable degree of accuracy by using only the ldquomainrdquo component pulse. This derivation has been very useful for reduced complexity demodulation of binary CPM signals. Subsequent to Laurent's work, it was shown that commensurate expressions could be obtained formultileveland multi-hCPM, but with an exponential increase in the total number of PAM component pulses in the signal representation. In this paper, we show that by expressing a CPM signal in its equivalent binary multi- form, we can derive a generalization of Laurent's result for the general class of such waveforms that use noninteger modulation indices. In this new signal representation, there is a clearly identifiable data-dependent ldquomainrdquo expansion pulse during each symbol interval which carries most of the signal energy. As in the Laurent Decomposition, the number of terms in this decomposition is only dependent on the CPM signal memory.

We consider a comparison of the Bhattacharyya bound and the Cramer-Rao lower bound for the problem of mobile positioning. Since the Cramer-Rao lower bound is known to be optimistic, we investigate the improvement that may be obtained by computing the third and fifth order Bhattacharyya bounds as alternative benchmarks for performance. The analytical results derived are then applied to the problem of locating an ultrawideband OFDM transmitter in a line of sight environment. Our results show that the third order and fifth order Bhattacharyya bounds respectively offer a 1.9 dB and a 2.3 dB improvement over the CRLB over the range of SNRs that have been deemed feasible for the ultrawideband system.

The future proliferation of UWB-enabled devices raises legitimate concerns for the impact of its use on the performance of incumbent radio systems. In this paper, we present analytical models that quantify the increase in forward traffic channel power allocation for the cdma2000 forward link in the presence of a single noise-like UWB interference source. Our analysis generally shows that protection of the cdma2000 forward link for indoor reception requires: (1) lowering of the UWB indoor emission limit so that it is below -73.3 dBm/MHz when the UWB transmitter is within 1 m of the victim handset (which is 20 dB below the FCC's currently specified indoor emission limit); or (2) operating the UWB device at a minimum separation of 5 m from the victim handset when it transmits at the indoor emission limit of -53.3 dBm/MHz.

Early channel reservation schemes have increasingly become more important for providing quality of services (QoS) in the All-IP network. In order to effectively provide the necessary QoS and optimize the channel management, we present an early channel reservation scheme based on mobile movement history. The basic principle behind this design is to view the reported sequence of location data as an encoding of a string of station-IDs. This sequence is reported by encoding the entire information of a sequence of traditional location registration messages using a dictionary, as in the LZ78 data compression algorithm. Results from information theory ensure that for mobile users with a steady and identifiable movement pattern, this prediction engine is capable of making highly accurate prediction in the long run, effectively achieving high hit ratio in early channel reservation. Finally, early channel reservation method is an important part of system network management. For better management of network resources, we consider the tradeoff between reserved channels and the level of guarantee that can be provided by the network based on the mobility profile.

This paper presents an inter-cell (hard) handoff algorithm that calculates adaptive handoff hysteresis values based on mobile location information and cell RF propagation statistics. The analysis is focused on the probability of handoff and the probability of dropped calls in the system. Simulation results show that the probability of unnecessary handoff is reduced using the adaptive handoff algorithm with only a minor increase in the dropped-call probability. This improvement is significant if the propagation signal varies rapidly in the cell.

This paper presents an adaptive soft handoff algorithm that dynamically calculates the threshold values for soft handoff based on mobile location, signal strength and RF propagation statistics. An analytical model has been previously developed to study the performance of an adaptive hard handoff method using mobile location information. We extend the adaptive hard handoff algorithm to study the performance of an adaptive soft handoff algorithm and also analyze the soft handoff considerations. Unlike conventional soft handoff algorithms, the threshold values for the adaptive soft handoff algorithm are chosen dynamically based on a set of quantitative descriptors for various propagation environments. Simulation results show that the adaptive soft handoff method reduces the unnecessary handoff probability and the number of base stations in the active set while still maintaining the call quality. This improvement is significant if the propagation signal varies rapidly in the cell or in the dense urban area.

The evolution to location-dependent services and applications in wireless systems continues to require the development of more accurate and reliable mobile positioning technologies. The major challenge to accurate location estimation is in creating techniques that yield acceptable performance when the direct path from the transmitter to the receiver is intermittently blocked. This is the non-line-of-sight (NLOS) problem, and it is known to be a major source of error in mobile location since it systematically causes the mobile to appear farther away from the base station than it actually is, thereby increasing the positioning error. We present a simple yet robust method for distinguishing between LOS and NLOS range measurements in a mixed measurement set and we validate its performance using simulations in several multipath channel environments.

The enhanced observed time difference (E-OTD) method is one of the emergency positioning technologies that has been standardized for GSM systems in the USA. In this paper, we apply the E-OTD approach to a (30 kHz) IS-136 TDMA system in order to study the effect of BTS clock drift on OTD estimation accuracy. We show that the presence of a constant BTS clock drift systematically biases the OTD estimates and causes the RMS OTD error to grow with increasing observation time.