5G networks are designed to support a variety of services with highly demanding Quality-of-Service (QoS) requirements. This opened the door for novel extended reality (XR) media applications to emerge with 5G. However, recent 5G field tests and system-level simulation studies show that further XR enhancements are required to support a massive adoption of XR services in 5G networks. Such enhancements are expected to come into play with 5G-Advanced. In this line, we propose and study an XR loopback mechanism that adapts the XR traffic to the instantaneous 5G network conditions by exploiting an XR application feedback. We propose various XR loopback algorithms, strategies, and parameters’ configurations and study their impact on the 5G end-to-end performance. We conduct extensive simulation campaigns by building realistic end-to-end 5G network scenarios with 3GPP mixed XR traffic setups. Results show that the proposed XR loopback mechanism can boost XR performance in 5G networks by adapting to 5G network conditions, while keeping the XR QoS requirements under control. We provide various insights and practical directions on XR loopback design that allow us to take full advantage of the 5G network capabilities and progress toward 5G-Advanced network design.

The effect of noise on the maximum useful number of receiver antennas that can be deployed in a cochannel interference diversity system is examined. The long term signal- power-to-interference-plus-noise-power ratio (SINRP), the long term signal amplitude to the square root of interference plus noise power ratio (SAINPR), the average instantaneous signal-to- interference-plus-noise ratio (AISINR), and the average bit error rate (BER) of a maximal ratio combining (MRC) diversity system in the presence of multiple cochannel interferers and additive white Gaussian noise (AWGN) are evaluated when the desired user signal and the interfering user signals are independent, and each of them experiences correlated Ricean fading at the receiver antennas. The results show that a previous design rule which states that the performance of a fixed-size antenna array containing the maximum number of independent antennas cannot be significantly improved by adding more than one additional antenna, still applies when the interference dominates the noise. It is shown that the SINRP and SAINPR measures exhibit asymptotic limits as the number of correlated antennas increases. Simple expressions for these limits are derived and it is shown that these asymptotic limits are unchanged when noise is neglected.

An exact and closed-form expression for the average bit error rate (BER) of coherent binary phase-shift keying (BPSK) using maximal ratio combining (MRC) in the presence of multiple cochannel interfering users is derived for correlated Rayleigh fading. Under the assumption that the branch gains of the desired user signal and interfering signals experience correlated Rayleigh fading with the same correlation eigenvector matrix, as is the case for receiver diversity in an omnidirectional scattering environment, this BER expression is valid for arbitrary correlation structure such as 2-D and 3-D channel correlation models, and applys for an arbitrary number of interfering users and an arbitrary number of receiver antennas.

An exact closed-form expression for the average bit error rate (BER) of coherent BPSK using maximal ratio combining (MRC) with correlated branches in the presence of cochannel interference (CCI) and noise is derived. This expression is valid for an arbitrary correlation structure under the assumption that the branch gains of the desired user signal and interfering signals experience correlated Rayleigh fading with the same correlation eigenvector matrix.

The symbol-error rate (SER) of a quadrature subbranch hybrid selection/maximal-ratio combining (QBHS/MRC) scheme for 1-D modulations in Rayleigh fading is examined. At the receiver, N diversity branches are split into 2N in-phase and quadrature subbranches. Traditional hybrid selection/maximal-ratio combining (H-S/MRC) is then applied over the 2N subbranches. M-ary pulse amplitude modulation, including coherent binary phase-shift keying, with QBHS/MRC is studied. The SER performances of QBHS/MRC and H-S/MRC are compared. Results show that QBHS/MRC systems outperform traditional H-S/MRC systems

The outage probability of maximal ratio combining diversity with an arbitrary number of antennas in the presence of an arbitrary number of cochannel interferers and thermal noise is derived when the branch gains of the desired user signal and interfering signals experience Rayleigh fading and have the same correlation matrix. Two special cases, when the correlation matrix is equicorrelated and when the correlation matrix has different eigenvalues, are considered for both the equal-power cochannel interference case and the unequal-power cochannel interference case. Further, the average bit-error rate of a coherent binary phase-shift keying (BPSK)-modulated cellular system using maximal ratio combining diversity in cochannel interference and correlated Rayleigh fading is derived. The effects of the average signal-to-noise ratio (SNR) and the average signal-power-to-interference-power ratio on the system performance are examined.

The question of how many receiver antennas to employ in a diversity system operating in cochannel interference is examined. The long term signal-power-to-interference-power ratio, the long term signal amplitude to the square root of the interference power ratio, the average instantaneous signal-to- interference ratio, and the average bit error rate of a maximal ratio combining diversity system in the presence of an arbitrary number of cochannel interferers are evaluated when the desired user signal and the interfering user signals experience correlated Ricean fading. The best number of antennas required for a fixed-size antenna array to achieve a good compromise between the system performance and system cost is investigated. The results show that, in general, the performance of a fixed-size antenna array containing the maximum number of independent antennas can not be significantly improved by adding more than one additional antenna. Some special cases where particular gains can be achieved by adding additional correlated antennas are also discusssed.

The outage probability and the average bit error rate of a coherent binary phase-shift keying modulated cellular system using maximal ratio combining diversity with an arbitrary number of antennas in the presence of an arbitrary number of cochannel interferers and thermal noise are derived when the branch gains of the desired user signal and the interfering signals experience Rayleigh fading and have the same correlation matrix. Two special cases, when the correlation matrix is equi-correlated and when the correlation matrix has different eigenvalues, are considered for both the equal-power cochannel interference case and the unequal-power cochannel interference case. The effects of the average signal-to-noise ratio, the average signal-to- interference ratio, and the correlation between antennas on the system performances are examined.

The exact performance of selection combining (SC), hybrid selection/maximal-ratio combining (H-S/MRC), and threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) in correlated Nakagami-m fading for positive integer values of fading parameter m, is analyzed for a particular correlation structure. This correlation model though not general, is much more general than the equal correlation case and includes equal correlation as a special case. The symbol error rate and outage probability of the three schemes are obtained by transforming the correlated branch gains into a set of conditionally independent branch gains. Numerical and simulation results show excellent agreement with theoretical results.

The average symbol error rate of threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) with correlated Nakagami-m fading channels is obtained for positive integer values of fading parameter m for a special correlation structure. An accurate approximate analysis of T-HS/MRC in arbitrarily correlated Nakagami-m fading channels is presented by using a Green's matrix approximation. The derivation allows different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying as an example

An accurate approximation to the average symbol error rate of hybrid selection/maximal-ratio combining (H-S/MRC) in correlated Nakagami-m fading with positive integer values of m, is obtained by using a Green's matrix approximation. This approach is valid for different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying (MPSK) as an example

An accurate approximation to the average symbol-error rate of hybrid selection/maximal-ratio combining (H-S/MRC) in correlated Nakagami-m fading with positive integer values of m is obtained by using a Green's matrix approximation. This approach is valid for different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying as an example.

The exact performance of selection combining, hybrid selection/maximal-ratio combining (H-S/MRC), and threshold-based H-S/MRC in correlated Nakagami-m fading for positive integer values of fading parameter m, is analyzed for a particular correlation structure. This correlation model, though not general, is much more general than the equal-correlation case, and includes equal correlation as a special case. The symbol-error rate and outage probability of the three combining schemes are obtained by transforming the correlated branch gains into a set of conditionally independent branch gains. Numerical and simulation results show excellent agreement with theoretical results

The average symbol-error rate of threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) with correlated Nakagami-m fading channels is obtained for positive integer values of fading parameter m for a special correlation structure. An accurate approximate analysis of T-HS/MRC in arbitrarily correlated Nakagami-m fading channels is presented by using a Green matrix approximation. The derivation allows different M-ary linear modulation schemes. We illustrate our methodology using M-ary phase-shift keying as an example.

The paper analyzes the average symbol error rate and outage probability of threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) in generalized fading environments. Using the moment generating function (MGF) method, a unified analysis of T-HS/MRC over various slow and frequency-nonselective fading channels is presented. Both independent, identically distributed and independent, nonidentically distributed diversity branches are considered. The derivation allows different M-ary linear modulation schemes. The theory is illustrated using coherent M-ary phase-shift keying in Nakagami-m fading as an example. It is shown that previously published results are incorrect.

A quadrature sub-branch hybrid selection/maximal-ratio combining (QBHS/MRC) scheme for one-dimensional modulations in Rayleigh fading is proposed. At the receiver, N diversity branches are split into 2N in-phase and quadrature sub-branches. Traditional hybrid selection/maximal-ratio combining (H-S/MRC) is then applied over the 2N sub-branches. The symbol error rate (SER) of M-ary pulse amplitude modulation (PAM), including coherent binary phase shift keying (BPSK), with QBHS/MRC is derived. The mean output signal-to-noise ratio (SNR) of a QBHS/MRC combiner is given. The performances of QBHS/MRC and H-S/MRC are compared. Results show that QBHS/MRC systems outperform traditional H-S/MRC systems.

The average symbol-error rate and outage probability of threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) in generalized fading environments are analyzed. A T-HS/MRC combiner chooses the combined branches according to a predetermined normalized threshold and the strength of the instantaneous signal-to-noise ratio (SNR) of each branch. Therefore, the number of combined branches is a random variable, rather than a fixed number, as in conventional hybrid selection/maximal-ratio combining (H-S/MRC). Using the moment generating function method, a unified analysis of T-HS/MRC over various slow and frequency-nonselective fading channels is presented. Both independent, identically distributed and independent, nonidentically distributed diversity branches are considered. The derivation allows different M-ary linear modulation schemes. The theory is illustrated using coherent M-ary phase-shift keying in Nakagami-m fading as an example. It is shown that previous published results are incorrect.