The fifth-generation (5G) new radio (NR) standard employs ultra-reliable and low-latency communication (URLLC) to provide real-time wireless interactive capability for the internet of things (IoT) applications. To satisfy the stringent latency and reliability demands of URLLC services, grant-free (GF) transmissions with the K-repetition transmission (K-Rep) have been introduced. However, fading fluctuations can negatively impact signal quality at the base station (BS), leading to an increase in the number of repetitions and raising concerns about interference and energy consumption for IoT user equipment (UE). To overcome these challenges, this paper proposes novel adaptive K-Rep control schemes that employ site diversity reception to enhance signal quality and reduce energy consumption. The performance evaluation demonstrates that the proposed adaptive K-Rep control schemes significantly improve communication reliability and reduce transmission energy consumption compared with the conventional K-Rep scheme, and then satisfy the URLLC requirements while reducing energy consumption.

Directions and speeds of the motion of rain areas are estimated for each type of rain fronts, using time differences detected in the rain attenuation of the Ku-band satellite radio wave signals that have been measured at Osaka Electro-Communication University (OECU) in Neyagawa, Osaka, Research Institute of Sustainable Humanosphere (RISH) in Uji, Kyoto, and MU Observatory (MU) of Kyoto University in Shigaraki, Shiga, for the past five years since September 2002. These directions and speeds are shown to agree well with those directly obtained from the motion of rain fronts in the weather charts published by Japan Meteorological Agency. The rain area motion is found to have characteristic directions according to each rain type, such as cold and warm fronts or typhoon. A numerical estimate of the effects of site diversity techniques indicates that between two sites among the three locations (OECU, RISH, MU) separated by 20-50 km, the joint cumulative time percentages of rain attenuation become lower as the two sites are aligned along the directions of rain area motion. In such a case, compared with the ITU-R recommendations, the distance required between the two sites may be, on an average, reduced down to about 60-70% of the conventional predictions.

The use of frequency-domain equalization based on minimum mean square error criterion (called MMSE-FDE) can significantly improve the bit error rate (BER) performance of DS-CDMA signal transmission compared to the well-known coherent rake combining. However, in a DS-CDMA cellular system, as a mobile user moves away from a base station and approaches the cell edge, the received signal power gets weaker and the interference from other cells becomes stronger, thereby degrading the transmission performance. To improve the transmission performance of a user close to the cell edge, the well-known site diversity can be used in conjunction with FDE. In this paper, we consider DS-CDMA downlink site diversity with FDE. The MMSE site diversity combining weight is theoretically derived for joint FDE and antenna diversity reception and the downlink capacity is evaluated by computer simulation. It is shown that the larger downlink capacity can be achieved with FDE than with coherent rake combining. It is also shown that the DS-CDMA downlink capacity is almost the same as MC-CDMA downlink capacity.

The downlink (base-to-mobile) bit error rate (BER) performance for a mobile user with relatively weak received signal in a multicarrier-CDMA (MC-CDMA) cellular system can be improved by utilizing the site diversity reception. With joint use of MMSE-based frequency domain equalization (FDE) and antenna diversity combining, the site diversity operation will increase the downlink capacity. In this paper, an expression for the theoretical conditional BER for the given set of channel gains is derived based on Gaussian approximation of the interference components. The local average BER is then obtained by averaging the conditional BER over the given set of channel gains using Monte-Carlo numerical method. The outage probability is measured from the numerically obtained cumulative distribution of the local average BER to determine the downlink capacity. Results from theoretical computation are compared to the results from computer simulation and discussed.

Single cell reuse of the same frequency, which is possible in DS-CDMA cellular systems, yields the option of site diversity to increase link capacity. In this letter, a generalized case of site diversity transmission is considered where multiple base stations (BS's) are involved in weighted transmissions with constant total transmit power to a target mobile station (MS). A general equation of conditional bit error rate (BER) is derived based on the model of weighted transmissions combined with antenna diversity reception and rake combining. It turns out theoretically that the optimum set of weights to maximize forward link capacity makes site selection diversity transmission (SSDT) the best performer. This theoretical analysis is confirmed by performance evaluation based on the Monte-Carlo simulation.

Similar to direct sequence code division multiple access (DS-CDMA), site diversity can be applied to a multicarrier-CDMA (MC-CDMA) cellular system to improve the bit error rate (BER) performance for a user with weak received signal power, thus resulting in an increased link capacity. In this paper, the downlink site diversity reception using frequency-domain equalization based on minimum mean square error (MMSE) is considered for a MC-CDMA cellular system. A set of active base stations to be involved in the site diversity operation is determined based on the received signal power measurement by a mobile station. Downlink capacity with site diversity is evaluated by computer simulation. The impacts of path loss exponent and shadowing loss standard deviation on the site diversity effect are discussed. Furthermore, the performance improvement by antenna diversity reception is discussed.

This paper investigates transmission power control for packet transmissions by using code division multiplexing (CDM) in the downlink common (shared) channel of CDMA cellular packet systems and proposes a transmission power control scheme to improve throughput performance and geographical fairness of communication services. In the proposed scheme, downlink transmission power is controlled based on the signal-to-interference ratio predicted at mobile stations. Throughput performance and transmission delay are evaluated under perfect power control conditions. Simulation results show that by using site diversity technique the proposed scheme improves the downlink throughput for light load conditions and geographical fairness for all offered channel loads under both non-fading and fading environments.

This paper evaluates the effect of inter-sector diversity with maximal ratio combining (MRC) coupled with coherent Rake combining and 2-branch antenna diversity reception in the transmit-power-controlled wideband direct sequence code division multiple access (W-CDMA) reverse link. We first elucidate based on laboratory experiments that the required average transmit signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average bit error rate (BER) of 10-3 with inter-sector diversity using two sectors is decreased by approximately 1.4, 1.0, and 0.2 dB compared to that with inter-cell site diversity using two cell sites with antenna diversity reception due to the superiority of MRC to selection combining (SC), when the difference in the average path loss between a base station (BS) and a mobile station (MS) is Δ12 = 0, 3, and 6 dB, respectively. We also clarify in actual field experiments that the inter-sector diversity associated with Rake time diversity and antenna diversity further decreases the required average transmit power of a MS if the number of resolved paths is small such as 1 or 2 in each sector reception, even when the fading correlation between sectors is relatively large. Furthermore, we show that the required average transmit power of a MS for satisfying the average BER of 10-3 with inter-sector diversity is decreased above approximately 2.0-2.5 dB compared to that with one-sector reception, owing to the significantly increased inter-sector diversity effect in addition to the Rake time diversity and antenna diversity, when the fading correlation averaged over the measurement course is approximately 0.7.

This paper proposes an inter-cell site diversity scheme based on 2-step selection combining (SC) and investigates through experimentation the effect of inter-cell site diversity in the transmit power-controlled wideband direct sequence code division multiple access (W-CDMA) reverse link. In the proposed algorithm, the decoded data sequence after soft-decision Viterbi decoding at each base station (BS) is transferred via the backhaul (wired line between BS and radio network controller (RNC) simulator) to the RNC simulator accompanied by reliability information of cyclic redundancy check (CRC) results per frame and the average signal-to-interference power ratio (SIR) calculated over the interleaving interval. The 2-step SC for each frame is performed at the RNC simulator using these two types of reliability information. We conclude from the laboratory experiments that the transmit power of a mobile station (MS) can be decreased since the selection period, TSEL, is shorter irrespective of the interleaving length, TILV, and that the required transmit power of a MS satisfying the average BER of 10-3 in inter-cell site diversity among 2 and 3 cell sites can be decreased by approximately 1.0 (0.5) dB and 1.3 (0.7) dB for fading maximum Doppler frequency fD = 5 (80) Hz, respectively, compared to a one-site connection (TILV = 80 msec, TSEL = 10 msec, path loss difference between 2 BSs and MS is 0 dB). We also confirmed by field experiments that the required transmit power of a MS in inter-cell site diversity between 2 cell sites can be decreased by approximately 2.0 dB compared to that of a one-site connection.

Multiple-site diversity systems are foreseen for earth to satellite paths operating at frequencies above 10GHz in localities with high rain-induced attenuation. In some severe cases double-site protection can be proved to be inadequate and consequently triple-site diversity becomes indispensable. In the present paper, an approach for the prediction of the triple-site diversity performance based on an appropriate three-dimensional gamma distribution is proposed. The model is oriented for application to earth-space paths located in Japan and other locations with similar climatic conditions. Numerical results are compared with the only available set of experimental data taken from some parts of the United States. Some useful conclusions are deduced.