Digital Twin (DT) technology has recently emerged as a powerful tool with the potential to revolutionize wireless systems as it enables accurate simulations, better decision-making, and tangible operational improvements. Prior studies on DT within the context of next generation wireless technologies has primarily focused on identifying potential use cases, application scenarios, and standardization challenges. However, the existing research lacks translating theoretical ideas into real-world applications. Our research, in this paper, contributes to the practical realization of DT technology in the context of 6G wireless networks, demonstrating its potential impact on network planning, performance, and user experience. In particular, we explore the construction, validation, and applications of DTs utilizing an indoor over-the-air (OTA) testbed powered by an in-house developed Next Generation Radio Access Network (NGRAN) that is fully compliant with 3rd Generation Partnership Project (3GPP) and Open RAN standards. First, we describe the steps that were followed to construct and validate a high-fidelity DT of our OTA testbed modeling both Radio Frequency (RF) environment and system components. Then, we demonstrate two pre-deployment use cases by explaining our extensive coverage estimation and network capacity planning OTA tests. Lastly, we also explore how DT enables practical machine learning solutions for post-deployment use cases and share our comprehensive OTA performance results, highlighting that our proposed mobility technique outperforms the classical approaches in terms of throughput and number of undesired handovers.

In this paper, we study the benefits of transmit and receive diversity for enterprise UMTS femtocell deployments. Indoor enterprise femtocell deployments face a single-path slow fading wireless environment that may lead to frequent hard handovers in the boundary region of neighboring femtocells and consequent degradation in the voice quality experienced by the users. In the absence of soft-handover (SHO) support, transmit diversity at the femtocell can combat single-path fading channel. We demonstrate through over-the-air tests that transmit diversity is very effective in reducing the number of hard handovers and therefore results in significant improvement in voice quality for enterprise users. On the uplink, we study system stability using an analytical approach. We derive analytical conditions for system stability with and without receive diversity at the femtocells. Using this analytical framework, benefits of receive diversity in maintaining system stability and preventing uplink power racing between neighboring femtocells are quantified. It is shown that, in the absence of SHO, receive diversity is very effective in maintaining system stability by preventing potential uplink power racing caused by inter-femto interference.

Downlink transmit power calibration is critical for femtocell deployment to achieve a good tradeoff between downlink coverage and interference impact to a co-channel macrocell network. In this paper, we study the performance of a femtocell power calibration algorithm that uses mobile reports to learn key information such as required coverage region for its own users and amount of interference to non-allowed users to fine-tune the femtocell downlink transmit power. It is shown that such a scheme is able to adapt to different deployment scenarios and provides better control of coverage-interference tradeoff than that provided by algorithms based on Network Listen Module alone.

Higher Order Modulation (HOM, 64-QAM) and Multiple Input Multiple Output (MIMO) transmissions are two key features introduced in the Release 7 (HSPA+) WCDMA systems to improve downlink performance. This paper focuses on the performance analysis of 64-QAM and MIMO in the WCDMA system. We describe the equalizer design for supporting these features as well as the simulation results demonstrating the higher system throughput and better user experience provided by these features.

Circuit-Switched (CS) Voice Services over HSPA (CSoHS) was recently introduced for 3GPP WCDMA Release 7/8 systems. The benefits of this feature include improving voice and data system capacity by utilizing the enhancements offered by the shared packet transport of HSPA air interface while preserving the already widely deployed core networks. In this paper, we discuss the operation and implementation of CSoHS and analyze its performance via simulations. We show that the system capacity of CSoHS is significantly higher than Release 99 CS voice under similar system conditions and voice quality.

We analyze the performance of voice services over 3GPP WCDMA networks for Release 99 and Release 7 deployments. We show, by using simulations, that the system capacity of Release 7 VoIP is significantly higher than the Release 99 circuit-switched voice under similar system conditions and voice quality. These results are obtained under the 3GPP simulation assumptions where uplink and downlink constraints for power, code and interference are considered. Both AMR 12.2 and 5.9 as well as different types of mobile receivers (Rake and equalizer, single and dual receive antennas) are considered. We also show that the capacity and performance can be increased significantly further by using uplink interference cancellation at the base station. The performance of best effort traffic in the presence of voice users is also analyzed.

We present a joint source-channel coding scheme based on incremental redundancy and feedback for transmission of real-time sources over wireless channels under strict delay constraints. The proposed scheme operates at constant bit rate and delay so as to capture the benefits of a feedback channel, while keeping the synchronous nature of pure forward error correction systems. We formulate the underlying Markov chain by introducing the notion of codetype and present a design algorithm for channel and source rate allocation. We present simulation results for speech transmission and show gains of up to 1 dB over pure FEC systems. We also present an application to CDMA networks and show increases of up to 28 % in the number of calls that can be simultaneously supported.

An embedded source code allows the decoder to reconstruct the source progressively from the prefixes of a single bit stream. It is desirable to design joint source-channel coding schemes which retain the capability of progressive reconstruction in the presence of channel noise or packet loss. Here, we address the problem of joint source-channel coding of images for progressive transmission over memoryless bit error or packet erasure channels. We develop a framework for encoding based on embedded source codes and embedded error correcting and error detecting channel codes. For a target transmission rate, we provide solutions and an algorithm for the design of optimal unequal error/erasure protection. Three performance measures are considered: the average distortion, the average peak signal-to-noise ratio, and the average useful source coding rate. Under the assumption of rate compatibility of the underlying channel codes, we provide necessary conditions for progressive transmission of joint source-channel codes. We also show that the unequal error/erasure protection policies that maximize the average useful source coding rate allow progressive transmission with optimal unequal protection at a number of intermediate rates.

We present a scheme for joint source-channel coding for transmission of sources compressed by embedded source coders over a memoryless noisy channel. We find an exact solution to the problem of optimal channel code allocation. Then we investigate the properties of the solution which allow us to transmit the source progressively while retaining the optimality at intermediate and final transmission rates, using rate-compatible codes.

When a feedback channel is available from the receiver to the transmitter, adaptive schemes for source-channel coding can be used for image transmission. In this paper we see that the use of embedded source codes and embedded channel codes, when combined in a hybrid ARQ protocol, can provide the desired flexibility at high efficiency, low complexity and low feedback channel usage. We propose optimized schemes for transmission over Gilbert-Elliot channels, with and without constraints on the feedback channel usage. We observe that the end-to-end quality of the received image can be improved significantly by a moderate use of feedback.

Summary form only given. We propose a joint source-channel coding scheme for the transmission of images over noisy channels. In this scheme, the interaction between source coding and channel coding is through a small number of parameters. A robust source coder based on the classification of the discrete wavelet transform (DWT) coefficients of the image is coupled with a flexible error control scheme which uses a bank of channel codes. Robustness in the source coder is achieved by scalar quantization of the coefficients followed by robust arithmetic coding to check catastrophic propagation of errors. Robust arithmetic coding generates a sequence of equal-length packets of bits along with a small number of sensitive bits for synchronization. A bank of rate compatible punctured convolutional codes concatenated with an outer error detection code like CRC is used for providing unequal error protection. Error detection is useful for error masking while decoding. The sensitive bits are protected and transmitted separately. An iterative algorithm is developed for selection of source coding rates and channel codes for the sequences of DWT coefficients. The algorithm uses the probabilities of packet decoding errors for the different channel codes and the operational rate distortion performance of the sequences of coefficients for the joint allocation. The system has a high reliability as the sensitive information is kept small. Some simulation results are provided for the transmission of the 512/spl times/512 image Lenna over binary symmetric channels.

In this paper we compare analog to digital conversion (ADC) delay in Hopfield ADC and asymmetrical (lower triangular) neural network-based ADC due to Avitabile et al. (1991). It is shown that, although Hopfield ADC has extensive feedback, its behavior in asynchronous mode is similar to that of lower triangular ADC. It is also shown that any constant delay n-bit feedforward ADC must have an exponential number of neurons.