This paper proposes a novel cloud-based approach for automated testing of Open Radio Access Network (O-RAN) systems, departing from traditional resource-intensive box-based testing methodologies to scalable pay-as-you-use remote testing. The proposed method encompasses hosting the O-RAN test system in the cloud, triggering an automation suite from an automation framework to execute a predefined set of test cases on the cloud-hosted system, and storing the test results along with key performance indicators (KPIs) in the cloud. A comprehensive automation framework has been developed, capable of executing thousands of test cases in the cloud environment. The framework comprises a front-end module hosted on a public cloud and a backend module hosted on either a private or public cloud, enabling seamless integration and efficient testing of O-RAN systems.

Massive multi-input multi-output (MIMO) is shown to significantly increase spectral efficiency by exploiting a large number of antennas to support high-order multiuser MIMO. In 3GPP Release-13, a full-dimension MIMO (FD-MIMO) technology was introduced to address practical aspects for massive MIMO in cellular systems; extensive simulations show 2–4 times capacity gain compared with current LTE systems. FD-MIMO has been identified as one of the key 5G technologies and is being continuously improved in 3GPP new radio standards. However, several practical challenges such as interference mitigation among MIMO streams for a large number of users with limited channel feedback, hardware limitations, such as calibration errors that limit the precoding capabilities need to be addressed carefully. A proof of concept (PoC) base-station and user equipment (UE) prototype has been designed to validate the potential of FD-MIMO technology and demonstrate commercial implementation feasibility. In this paper, we present theory and architecture behind an FD-MIMO prototype and share the field test results with LTE-based UEs in a multi-user MIMO setup. We also analyze the impact of transmitter and receiver calibration errors on the performance of the FD-MIMO system.

We consider analog multiband as a means for scaling up the bandwidth for millimeter (mm) wave communication. Analog multiband sidesteps the difficulty of scaling analog-to-digital conversion (ADC) to higher sampling rates by channelizing the available bandwidth in the analog domain into subbands and using existing power-efficient ADCs to digitize each subband. In this paper, we address the issue of efficient channelization into subbands. A direct approach using a bank of mixers with independent frequency synthesizers has several disadvantages, including large power consumption and the potential for oscillator coupling. We explore an alternative approach based on polyphase sampling, using analog discrete Fourier transform (DFT) along with appropriately designed baseband filters. We quantify the inter-subband interference as a function of filter choice, and demonstrate that it can be handled using interference suppression strategies developed in our prior work. A natural comparison of such approaches, where analog channelization is followed by parallel ADCs running at slower rates for each subband, is with time-interleaved ADCs, which also use polyphase samplers, but use parallel sub-ADCs to digitize the entire band. We show that the proposed approach reduces the required dynamic range of the subband ADCs in comparison to the TI-ADC.

Designing millimeter wave (mmWave) cellular system with good coverage necessitates the use of directional beams to transmit synchronization signals in the system, and with that comes several challenges. In this paper, we present a detailed synchronization channel (SCH) design for mmWave systems. We provide a link-budget study to determine the minimum required transmit and receive beamforming gains. We also present designs for the SCH pattern in the frame structure. We design SCH sequences and show that our design provides a 3 dB better performance than LTE under similar conditions. Moreover, we propose a method is based on a genetic algorithm, to efficiently synthesize the beams required to transmit SCH.

Dual-polarized antennas provide a mechanism to achieve polarization diversity or multiplex non-interfering data streams over-the-air. Practical realization of dual-polarized transmission, however, must overcome challenges such as mobile misorientation with respect to the base station as well as non-ideal polarization isolation. With the advent of mmWave communications, dual-polarized large scale antenna arrays can be realized inexpensively. In this paper, we propose a beamforming algorithm that jointly designs the horizontal and vertical beamformers and combiners to maximize spectral efficiency in the presence of mobile misorientation and polarization leakage. First, we show that dual-polarized antenna arrays introduce channel structure that enables mobile orientation estimation without explicit channel knowledge. We derive the maximum likelihood estimate of the azimuth and elevation mobile rotation. Given these estimates, we design the horizontal and vertical beamformer and combiner with practical RF hardware constraints. We generalize the beamforming algorithm to enable multiplexing multiple data streams across different channel paths in the horizontal and vertical domain. Results show that mobile orientation estimation using dual-polarized antenna arrays achieves over 90% accuracy even below 0 dB. Using a realistic clustered channel model, spectral efficiency gains of the order of 5 dB are demonstrated over dual-polarized antennas with independent horizontal/vertical beam steering as well as single polarized antenna arrays.

Next generation wireless backhaul systems may provide data rates exceeding 10 Gb/s using large bandwidth available at mmWave frequencies, and support features such as point-to-multipoint communication, non-line-of-sight communication, in-band operation (shared spectrum with access) and inter-BS coordination. We explore the feasibility of an “in-band” mmWave wireless base-station with the option of enabling backhaul transmission on one panel while simultaneously receiving access or backhaul on an adjacent panel. We show using simulations and lab measurement validation, that for a prototype 28 GHz mmWave system, the self-interference from the TX sector panel to the adjacent RX panel is around -70 to -80 dB and an additional 35-50 dB isolation is needed for enabling reception on adjacent RX panel that may be achieved through full duplex interference cancellation techniques.

In this paper we propose a new dual quantization-domain LDPC decoder, which requires only 3-bit messages between the check nodes and the variable nodes. To reduce complexity and save power, check nodes processing is entirely in the 3-bit domain. However, to avoid loss in performance, the variable nodes processing is in a higher bit precision domain. A non-linear mapping is used to map the messages from one quantization domain to the other. Simulations and hardware evaluation of the proposed decoder showed greater than 50% reduction in power consumption with only 0.1 dB (0.2 dB) loss in bit-error-performance when compared to a reference 5-bits scaled Min-Sum decoder over the AWGN (fading) channel.

Wireless LAN systems have been continuously evolving to provide ~10X increase in data rates every five years, exploiting higher mmWave frequencies and larger bandwidths, such as IEEE 802.11ad, providing 6.76 Gb/s using 2.16 GHz of bandwidth at 60 GHz. One of the key technical challenges to successful commercialization of these large bandwidth systems is power consumption. In this paper, we focus on reducing the idle listening mode power consumption where the device is actively looking for packets and the power consumption is dominated by the high speed ADCs. We propose a low power and bandwidth-scalable synchronization design for large bandwidth systems by developing reduced bandwidth modes in high-speed ADCs used in such systems. We study the impact of the proposed synchronization design on the detection probability, false alarm, AGC design and symbol timing estimation. Comparisons of our design using a bandwidth reduction of 4 with the existing IEEE 802. Had synchronization design show no loss in AWGN and a 0.8 dB loss in fading for an equivalent acquisition time and false alarm rate while providing a 33% power reduction in idle mode, assuming the ADCs consume 50% of the total idle power consumption. We also provide backward compatibility with current IEEE 802.11ad systems with limited impact on performance and power consumption.

We propose an approach to scaling communication bandwidths over dispersive channels that preserves the advantage of DSP-centric receiver design, while sidestepping the difficulty of scaling analog-to-digital conversion (ADC) to higher and higher bandwidths. This is accomplished by channelizing the available bandwidth into contiguous subbands in the analog domain, with the width of a subband chosen so that digitization is possible at reasonable cost and power using existing ADC technology. We illustrate these ideas for multiGigabit indoor mm-wave communication, with GHz bandwidth divided into subbands of width 250-500 MHz. The channel delay spread even after beamforming can be as large as 20 ns, hence the channel seen within subbands is dispersive. Further, the contiguity of subbands and the sloppy analog channelization implies that adjacent subbands interfere with each other. We show that OFDM within subbands is an attractive approach in these settings: the channel dispersion within subbands can be handled with a moderate cyclic prefix, while the inter-band interference manifests itself only on the edge subcarriers. We clarify the structure of the inter-band interference, and show that it is effectively suppressed by adaptive linear Minimum Mean Squared Error (MMSE) techniques for joint detection across adjacent subbands. Our performance evaluation is carried out using channel models developed for the IEEE 802.1 lad 60 GHz standard.

Millimeter wave (mmWave) signals experience orders-of-magnitude more pathloss than the microwave signals currently used in most wireless applications and all cellular systems. MmWave systems must therefore leverage large antenna arrays, made possible by the decrease in wavelength, to combat pathloss with beamforming gain. Beamforming with multiple data streams, known as precoding, can be used to further improve mmWave spectral efficiency. Both beamforming and precoding are done digitally at baseband in traditional multi-antenna systems. The high cost and power consumption of mixed-signal devices in mmWave systems, however, make analog processing in the RF domain more attractive. This hardware limitation restricts the feasible set of precoders and combiners that can be applied by practical mmWave transceivers. In this paper, we consider transmit precoding and receiver combining in mmWave systems with large antenna arrays. We exploit the spatial structure of mmWave channels to formulate the precoding/combining problem as a sparse reconstruction problem. Using the principle of basis pursuit, we develop algorithms that accurately approximate optimal unconstrained precoders and combiners such that they can be implemented in low-cost RF hardware. We present numerical results on the performance of the proposed algorithms and show that they allow mmWave systems to approach their unconstrained performance limits, even when transceiver hardware constraints are considered.

Millimeter wave (mmWave) systems must use beamforming to overcome the heavy attenuation at mmWave frequencies and establish high-quality communication links with reasonably high spectral efficiency. When received signal power is sufficiently large and the propagation channel is sufficiently rich, beamforming with multiple data streams, known as precoding, could further increase data rates in mmWave systems. The high cost of digital devices in mmWave systems, however, implies that precoding is predominantly done in the analog domain, making mmWave precoding significantly more constrained than traditional multiple-input multiple-output (MIMO) solutions. In this paper, we propose an iterative precoding algorithm for a practical mmWave transmitter architecture in which all precoding is done in the analog domain. In addition to precoding, the proposed algorithm allows the mmWave system to adapt the rank of its transmission in response to varying propagation conditions. We present numerical results showing that the proposed multimode precoding algorithm allows systems to achieve large data rates, in some cases approaching channel capacity.

Millimeter wave (mmWave) systems must overcome heavy signal attenuation to support high-throughput wireless communication links. The small wavelength in mmWave systems enables beamforming using large antenna arrays to combat path loss with directional transmission. Beamforming with multiple data streams, known as precoding, can be used to achieve even higher performance. Both beamforming and precoding are done at baseband in traditional microwave systems. In mmWave systems, however, the high cost of mixed-signal and radio frequency chains (RF) makes operating in the passband and analog domains attractive. This hardware limitation places additional constraints on precoder design. In this paper, we consider single user beamforming and precoding in mmWave systems with large arrays. We exploit the structure of mmWave channels to formulate the precoder design problem as a sparsity constrained least squares problem. Using the principle of basis pursuit, we develop a precoding algorithm that approximates the optimal unconstrained precoder using a low dimensional basis representation that can be efficiently implemented in RF hardware. We present numerical results on the performance of the proposed algorithm and show that it allows mmWave systems to approach waterfilling capacity.

Visible Light Communication (VLC) is a short range wireless transmission of visible light through free space. The light source can be based on Light-Emitting Diodes (LEDs), that are becoming common use in our future connected home where they can be simultaneously used for both illumination (i.e. LED TVs, Light bulbs, etc.) and communication with appropriate photodiodes in the receiver side. VLC can be adapted to mobile devices enabling new types of short range applications such as HD video streaming. However, many of the new emerging mobile applications require increasingly high data rates; some can even exceed 1 Gbps. In this paper, we propose new optical/electrical front-end and baseband systems that achieve the required bit rate of 1 Gbps over free space. We also detail the implementation challenges of the low power VLC communication system for a mobile device. Specifically we focus on the new VLC baseband system and propose new baseband scheme with state-of-the-art LDPC channel coder. Finally, we will present the results of the new proposed gigabit baseband system as well as lab test results of a single channel VLC front-end running at 540 Mbps and 1080 Mbps.

Consideration of mmWave frequencies with large phased antenna arrays has become increasingly important for providing multi-Gb/s wireless data communication. However, large phased antenna arrays tradeoff gain for very narrow beam widths, which may not always be desirable for outdoor, mobile communication. This paper provides a systematic approach for beam broadening for phased antenna arrays, with unit amplitude constraint and without turning off antennas, using multi-beam subarrays and without any increase in hardware complexity. We first show that the beam resulting from the full array lies in the region defined by the sum of the individual subarrays and beams can be shaped within the region using RF or baseband phase precoding. While both conjugating and flipping the weights for subarrays generate similar subarray responses, only flipping the weights guarantees a symmetric response of the full array about boresight. We develop expressions for the resultant array factor, the locations for the beam directions of the subarrays and the half power beam width of resulting beam. We show that the broadening factor is proportional to the square of number of subarrays and the final array can be designed to have less than a 3 dB ripple in the passband.

Due to the scarcity of spectrum below 3 GHz for wireless communications, there have been proposals to explore millimeter wave (mmWave) spectrum (3- 300 GHz) for commercial mobile applications. MmWave spectrum provides unique advantages such as availability of GHz bandwidth and use of antenna arrays with beamforming to compensate for path loss. While there exist well-established models for mmWave indoor non-line-of-sight (60 GHz) and mmWave outdoor line-of-sight (backhaul) communication, mmWave channels for outdoor, non-line-of-sight, mobile communication have not been explored sufficiently. We present penetration and reflection measurements for different materials and line-of-sight and non- line-of-sight measurements for outdoor mmWave mobile communication. We find that while well-known lossy objects such as human body and concrete can have poor penetration, they are good reflectors at these frequencies, enabling the receiver to capture secondary reflections for non-line-of-sight communication. We also show that a wide beam width, low gain antenna at the mobile receiver can capture more energy in scattered non-line-of-sight environments and thus, can provide more gain than a narrow beam, high gain antenna for mobile communication. Our initial measurements motivate utilizing mmWave frequencies for outdoor non-line- of-sight mobile communication.

Security concerns about the Smart Grid are becoming more prevalent as the deployment of grid becomes more widespread. In this paper, we propose secure and intuitive device authentication techniques for the Smart Grid enabled Home Area Networks (HANs). We assume a distributed architecture for the HAN which consists of the smart appliances, the smart meter and the gateway. In this architecture, the operating schedules of the appliances are controlled by the gateway based on the pricing and control messages from the smart meter. We propose three different authentication mechanisms for devices in the HAN: 1) between the gateway and the smart meter, 2) between the smart appliances and the HAN, and 3) between the transient devices and the HAN. We show that the adversarial behavior during the authentication of devices such as the man-in-the-middle and impersonation attacks are prevented using the proposed device authentication mechanisms by extensive use of collaboration between different parties. Eventually, we provide secure and intuitive device authentication mechanisms (that require minimum or no user effort) for various parts of the HAN with low computation and communication overheads.

Almost all cellular mobile communications including first generation analog systems, second generation digital systems, third generation WCDMA, and fourth generation OFDMA systems use Ultra High Frequency (UHF) band of radio spectrum with frequencies in the range of 300MHz-3GHz. This band of spectrum is becoming increasingly crowded due to spectacular growth in mobile data and other related services. More recently, there have been proposals to explore mmWave spectrum (3-300GHz) for commercial mobile applications due to its unique advantages such as spectrum availability and small component sizes. In this paper, we discuss system design aspects such as antenna array design, base station and mobile station requirements. We also provide system performance and SINR geometry results to demonstrate the feasibility of an outdoor mmWave mobile broadband communication system. We note that with adaptive antenna array beamforming, multi-Gbps data rates can be supported for mobile cellular deployments.

This paper provides mechanisms to support fast and energy-efficient link recovery for optical communication using visible light spectrum. Visible light communication (VLC) is becoming increasingly important to support low power, Gbps data rate communications due to the recent advances in LED technology and high power consumption needed for sampling and processing Gbps data in baseband for RF communication systems. In VLC, the line of sight and high directional feature make the fast link recovery a key issue. Fast link recovery is a new challenge for reliable VLC. This paper presents fast and energy-efficient link recovery approaches for VLC local area network and peer-to-peer communications, with further enhancements for multiple communication directions and color bands. The proposed approaches can achieve link recovery timely, and save the battery life of VLC devices.

Truncation in digit-precision is a very important and common operation in embedded system design for bounding the required finite precision and for area-time-power savings. In this paper, we present the use of online arithmetic to provide truncated computations with communication systems as one of the applications. In contrast to truncation in conventional arithmetic, online arithmetic can truncate dynamically and produce both area and time benefits due to the digit-serial nature of computations. This is of great advantage in communication systems where the precision requirements can change dynamically with the environment. While truncation in conventional arithmetic can have significant truncation errors, especially when the output precision is less than the input precision, the redundancy and most significant digit first nature of online arithmetic restricts the truncation error to only the least significant digit of the truncated result. As an application that uses significant truncation in precision, a code matched filter detector for wireless systems is designed using truncated online arithmetic. The detector can provide both hard decisions and soft(er) decisions dynamically as well as interface with other conventional arithmetic circuits or act as a DSP coprocessor. Thus, optimized communication receivers with coexisting conventional arithmetic for saturation and online arithmetic for truncation can now be built. The truncated online arithmetic detector was also verified with a VLSI implementation in an AMI 0.5 mu MOSIS tiny chip process

This paper presents algorithms and architecture designs that can meet real-time requirements of multiuser channel estimation and detection in future code-division multiple-access-based wireless base-station receivers. Sophisticated algorithms proposed to implement multiuser channel estimation and detection make their real-time implementation difficult on current digital signal processor-based receivers. A maximum-likelihood based multiuser channel estimation scheme requiring matrix inversions is redesigned from an implementation perspective for a reduced complexity, iterative scheme with a simple fixed-point very large scale integration (VLSI) architecture. A reduced-complexity, bit-streaming multiuser detection algorithm that avoids the need for multishot detection is also developed for a simple, pipelined VLSI architecture. Thus, we develop real-time solutions for multiuser channel estimation and detection for third-generation wireless systems by: (1) designing the algorithms from a fixed-point implementation perspective, without significant loss in error rate performance; (2) task partitioning; and (3) designing bit-streaming fixed-point VLSI architectures that explore pipelining, parallelism, and bit-level computations to achieve real-time with minimum area overhead.

This paper demonstrates the advantages of using online arithmetic for traditional and advanced detection algorithms for communication systems. Detection is one of the core computationally-intensive physical layer operations in a communication receiver and determines the communication data rates. Detection algorithms typically involve hard decisions (sign based testing) to find the sign of the transmitted information bit. This results in extraneous computations in a conventional number system as the sign is obtained only at the end due to the least significant digit first (LSDF) nature of computations. Online arithmetic, based on a signed digit number representation, provides most significant digit first (MSDF) computation. Hence, the computations can stop after the first non-zero MSD (sign) is computed and additional computations for the successive digits can be avoided. Back-conversion to a conventional number system is not required as the sign of the digit represents the detected bit. A comparison of a radix-4 serial digit on-line multiuser detector with an 8-bit parallel conventional arithmetic multiuser detector shows a decrease in latency by 1.79X, a 3X increase in throughput, and possible savings in area.

A real-time VLSI architecture is designed for multiuser channel estimation, one of the core baseband processing operations in wireless base-station receivers. Future wireless base-station receivers will need to use sophisticated algorithms to support extremely high data rates and multimedia. Current DSP architectures are unable to fully exploit the parallelism and bit level arithmetic present in these algorithms. These features can be revealed and efficiently implemented by task partitioning the algorithms for a VLSI solution. We modify the channel estimation algorithm for a reduced complexity fixed-point hardware implementation. We show the complexity and hardware required for three different area-time tradeoffs: an area-constrained, a time-constrained and an area-time efficient architecture. The area-constrained architecture achieves low data rates with minimum hardware, which may be used in pico-cell base-stations. The time-constrained solution exploits the entire available parallelism and determines the maximum theoretical data rates. The area-time efficient architecture meets real-time requirements with minimum area overhead. The orders-of-magnitude difference between area and time constrained solutions reveals significant inherent parallelism in the algorithm. All proposed VLSI solutions exhibit better time performance than a previous DSP implementation.