Cell phone battery life has been a fundamental design consideration ever since the first mobile devices were introduced in the 1970's. When mobile services were restricted to voice, the problem from a system design perspective often boiled down to finding best of breed components (e.g. amplifiers, signal processors, etc.) that optimized power while not sacrificing size. However, today's cell phones support a wide array of services beyond voice telephony, and battery life optimization is now being considered with respect to each of this multitude of services. Optimizing battery life for internet usage is a less constrained problem than optimization for voice telephony or audio and video playback. For starters, it is difficult to optimize the hardware in a mobile phone for a specific internet service given that there are many different types of services available over the internet (email, web, etc.). Nevertheless, almost all popular internet services that do not require a guaranteed level of quality-of-service (e.g. VoIP) can be delivered as web services wireless settings. As a result, power optimization in web transport mechanisms is an attractive area of focus for internet power optimization. In this work, the use of a mobile web proxy is considered as a means of increasing handset battery life for mobile web browsing. By leveraging observed user interaction with web content, the proxy can be designed to improve power consumption without sacrificing user experience.

Cellular data services have benefited recently from enhancements in access speed, delay, and other parameters generally associated with quality-of-service (QoS). However, end users still often have trouble discovering appropriate content due to fractured and non-intuitive approaches to content discovery. One possible means of addressing this problem is the use of recommender systems to personalize content for cellular data users. Recommender systems have an established role in internet content discovery, but their applications in wireless are not straightforward. This paper discusses the critical challenges in implementing recommender systems for content in cellular systems, and also proposes methods for deployment of such systems so as to improve content discovery.

Dense multipath fading associated with ultra-wideband (UWB) channel presents technical challenges for reliable communication. To adapt to this radio environment efficiently, we use pilot aided UWB technology with transmitted reference spread spectrum scheme. We analyze IEEE 802.15 UWB channel's characteristic, the trade-off between the signal energy capture and the interference-plus-noise energy for different reference signals, where every reference signal is a partial waveform of the composite channel. Given the channel condition, we find a reference signal that minimizes the bit error probability (BEP). We show that using the optimum reference signal instead of the composite channel as the correlator template, one can significantly lower the BEP depending on the channel condition.

Fast closed-loop power control is widely used in code division multiple access (CDMA) systems to ensure a minimum received signal quality for circuit-switched services, foremost among which is voice. However, third-generation wireless systems such as cdma2000 often accommodate multiple concurrent services with different quality-of-service constraints. Nevertheless, typical closed loop power control methods still are biased towards only one service. In the cdma2000 reverse link, concurrent services may be accommodated over code-multiplexed channels (namely the fundamental channel FCH and supplemental channel SCH). This paper provides a method for optimizing power control for the SCH in the presence of an FCH when a radio link protocol (RLP) is used. This method achieves less transmission power in most of cases, as well as less RLP delay

Physical limitations due to fading and interference in wireless channels pose technical challenges in achieving reliable communication. To adapt to this adverse radio environment efficiently, we propose a fade-resistant transmission system based on code division multiple access (CDMA) technology. In this system, all the symbols of a user are transmitted simultaneously using parallel sequences over a time-varying wireless channel. We derive the relationship between the self-interference and the multiple-access interference in such a system. We prove that instantaneous signal-to-interference-plus-noise ratio (SINR) at the matched filter output of a system with parallel sequences is statistically higher than that of the conventional CDMA system. Numerical results demonstrate that the parallel sequence transmission scheme can provide capacity improvement over the conventional CDMA system depending on variations in the channel.

The success of Wi-Fi and emergence of Wi-MAX creates exciting technology and business challenges for the communication industry. Roaming, seamless voice and data hand-offs, in conjunction with continuity of voice services such as messaging, push-to-talk, and voicemail, are posing the next technology and business challenges. Services convergence among Wi-Fi, Wi-MAX, and cellular networks is creating opportunities for both wireless, and wireline service providers. Similar opportunity exists for enterprises for the first time. Services convergence can give enterprises the freedom similar to "PBX"es for wireless access on and off campuses. As the business cases for enterprises and wireline service providers are pitted against each other on the commercial front, the technologies will evolve out of market leverage, presence and acceptance. This poses a challenge for technologists to create a technology that is easily deployable in target scenarios. The requirements exist for a solution that, independently of the end user and service providing entity, can fulfil the "service quality" expectations of users and providers. In this talk, we discuss the requirements of voice service convergence solutions, protocols, standardization effort, and challenges for solution development. We also allude to the opportunities for research and development of newer technologies. These innovations will breach the current gaps in convergence of services beyond packet to circuit call control mechanisms and extend them across different access technologies, such as Wi-Fi, Wi-MAX, GSM, CDMA, and others.

To adapt to the adverse radio environment efficiently, we address the use of a pilot aided multicode code division multiple access (CDMA) system. This system is implemented by transmitting all the information symbols together with the pilot symbols of a user simultaneously over the wireless channel. We analyze the trade-off between the diversity order and the channel estimation error in the performance of the proposed system. Our numerical results indicate that depending on the transmitter power and the channel condition, the proposed system is capable of outperforming the conventional CDMA system with known channel state information at the receiver.

In this paper, we study the reliability as offered jointly by the medium access control (MAC) and the radio link protocol (RLP) for third generation (3G) code division multiple access (CDMA) standards. The retransmission mechanism supported at the RLP layer has a considerable amount of delay (80-100 ms) associated with it; hence, it may not be able to support applications with strict delay requirements. On the other hand, if retransmissions are also performed at a lower layer, such as the MAC layer, then the performance of CDMA systems can be improved because of the fast retransmissions at the MAC layer. We show how the performance of RLP improves with respect to three metrics - mean delay, throughput, and RLP recovery -when a finite number of retransmissions is allowed at the MAC layer. Synthetically generated Web traffic is used as the application, the objects of which are fragmented into equal-sized RLP frames. We consider soft packet combining support at the receiver, which effectively lowers the frame error rate. We also consider the possibility of misinterpretations of acknowledgments. Simulation experiments are conducted to verify the performance as offered jointly by the MAC and the RLP, particularly for cdma2000 standard and wideband CDMA (WCDMA) systems. The improvement in the TCP throughput is also evaluated.

In this paper, we propose a novel channel quality indicator (CQI) measure for the space-time jointly encoded MIMO-CDMA systems in frequency selective channels. The CQI proposed here is derived from a so-called per-Walsh code joint detection structure consisting of a front-end linear filter followed by joint symbol detection across all streams. The linear filter is designed to convert the multipath channel into a single-path channel to restore orthogonality of Walsh codes and to avoid joint sequence detection. We derive a class of filter that maximizes the so-called constrained mutual information, and show that the conventional LMMSE and MVDR equalizers belong to this class. Similar to the notion of generalized SNR (GSNR), this constrained mutual information provides us with a CQI measure describing the MIMO link quality. Such a CQI measure is essential in providing a simple one-dimensional mapping for both link adaptation and link-to-system mapping for jointly encoded MIMO-CDMA system.

The capacity of a wireless system is subject to bandwidth constraints, fading, as well as temporal and spatial variations in data traffic. To adapt to this adverse radio environment efficiently, we propose a fade resistant transmission system using parallel sequences. Our analysis shows that instantaneous signal-to-interference-plus-noise ratio at the matched filter output of the proposed system is statistically higher than that of the conventional system. Numerical results demonstrate that the proposed parallel sequence transmission scheme can provide capacity improvement over the conventional system depending on variations in the channel.

A method for using the discrete cosine transform (DCT) as an alternative to the discrete Fourier transform (DFT) for orthogonal frequency division multiplexing (OFDM) wireless transmission methods is presented. These transforms satisfy the cyclic convolution properties of the DFT when used with a symmetric extension. Analysis of intersymbol and intercarrier interference in OFDM systems reveals that under certain channel conditions, throughput is enhanced when using the DCT rather than the DFT.

We study the joint reliability as offered by the medium access control (MAC) and the radio link protocol (RLP) in CDMA systems, particularly for 1XTREME. The retransmission mechanism in the RLP has considerable amount of delay associated with it which might not be able to sustain real-time communications with strict delay requirements. Retransmissions done at a lower layer, such as the MAC, enhances the performance of the system. We show how the performance varies with respect to delay and throughput as observed from the RLP, for finite number of retransmissions at the MAC. We find that there is a substantial gain in the performance with the incorporation of fast retransmissions at the MAC. Synthetically generated HTTP traffic was used as the application, the objects of which were fragmented into equal sized RLP frames. We consider an I-path Rayleigh fading channel with correlated errors. We also consider that soft packet combining at the receiver is supported, which effectively lowers the frame error rate (FER). Simulation experiments are conducted to verify the performance as offered by the MAC and the RLP.

We study the reliability as offered jointly by the medium access control (MAC) and the radio link protocol (RLP) for CDMA systems, particularly for the cdma2000 evolution standard cdma2000 1-EV. The retransmission mechanism in the RLP has a considerable amount of delay associated with it which might not be able to sustain real-time communications with strict delay requirements. Retransmissions done at a lower layer, such as the MAC, enhances the performance of the system. We show how the performance varies with respect to delay and throughput as observed from the RLP, for finite number of retransmissions at the MAC. We also consider that soft packet combining at the receiver is supported, which effectively lowers the frame error rate (FER). Simulation experiments have been conducted where synthetically generated HTTP traffic was used as the application, the objects of which were fragmented into equal sized RLP frames before being transmitted over the wireless channel. We observe that the the delay and the RLP retransmissions are low enough to sustain real-time communications with the incorporation of fast retransmissions at the MAC layer.

A method of packet scheduling is proposed wherein the transmitter schedules packets to be sent out based on received power control feedback in a CDMA system. By taking advantage of implicit link quality feedback from the receiver in the form of power control commands, the transmitter may reduce the number of retransmissions necessary for any individual packet by sending it when channel conditions warrant adequate delivery conditions. Simulation results are provided which demonstrate the proposed method's effectiveness.

The transmit adaptive array (TxAA) is one of the promising closed-loop downlink diversity schemes being considered for the third generation wireless systems based on code division multiple access (CDMA). The TxAA technique originally proposed, requires a user-specific auxiliary pilot for coherent demodulation. This affects the capacity of the system due to additional power being used by this pilot. The mobile receiver requires additional hardware correlators for demodulating the pilot. Since different channels in spread spectrum systems are distinguished by their spreading sequences, it also uses up an additional Walsh code per user. This paper proposes a decision directed method for demodulation which does not require a user-specific pilot. Our simulations demonstrate that the performance of the technique is comparable to that of the method based on a user specific pilot.

A method of averaged diversity combining of packets for a wideband CDMA (WCDMA) system is presented. This method entails the use of blind retransmission identification at the receiver to overcome the need for other throughput-reducing schemes for retransmission identification. Simulation results are provided which demonstrate the usefulness of the proposed method.

Currently, two 3rd-generation CDMA (code division multi access) systems have been standardized. The UMTS (Universal Mobile Telecommunication System) adopts W-CDMA (wideband CDMA) direct spread (DS) air interface and the cdma2000 system adopts the cdma2000 multicarrier (MC) air interface. Currently the UMTS system is connected to a GSM-MAP based network protocol and the cdma2000 system is connected to an ANSI-41 based network protocol. There are ongoing harmonization efforts to cross-connect the W-CDMA DS to the ANSI-41 based network (the "DS-41" air interface) and the cdma2000 MC to the GSM-MAP based network (the "MC-MAP" air interface). The DS-41 air interface uses the physical layer, link layer and the radio resource control of W-CDMA DS but uses the mobility management and call control of the cdma2000 system. On the other hand, the MC-MAP uses the physical layer, link layer and the radio resource control of cdma2000 MC but uses the mobility management and the call control of the W-CDMA DS. This paper discusses the necessary DS-41 modifications, particularly with respect to the authentication procedure. This paper also considers the authentication procedures during roaming between the DS-41 and the UMTS systems. Call flows are presented to support the studies.

In a cdma2000 system, typically a radio-link protocol (RLP) is defined below a TCP/IP application to account for variations in the wireless channel that normally cannot be handled by TCP. RLP runs in a non-transparent mode all times, implying that delay-sensitive applications utilizing RLP may suffer due to the predefined method of automatic repeat request (ARQ). In this proposal, a method of power control to increase the reliability of RLP retransmissions is proposed, which reduces the RLP frame error rate (RLP-FER). Using simulation data, it is also demonstrated that the proposed method has little effect on capacity.

A two-stage lossless image compression scheme is presented, the first stage of which decorrelates the raw image data by using a two-dimensional, causal linear predictor, resulting in significant entropy reduction. The second stage uses standard coding techniques. Different two-stage schemes are compared with respect to their performances on several images, using bilevel coding, arithmetic coding, and adaptive Huffman coding.