Capacity gains for each effective reuse factors.

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... freq is the IV. total S IMULATION number of frequencies R ESULTS and TRX − avg is The the average network number capacity of assessment TRX per was sector made [13]. based on Block- ing The Rate only (BCR) codec and used Bad was Quality the AMR-590, Call rate since (BQC), it is which a good is indicator of the achievable performance for the simulated cases. Simulation test cases included usage of AMR FR, AMR HR and AMR DHR channel modes as well as SAIC and non-SAIC receivers. Table II shows characteristics of each test case. IV. S IMULATION R ESULTS The network capacity assessment was made based on Block- ing Rate (BCR) and Bad Quality Call rate (BQC), which is the percentage of users with Frame Erasure Rate (FER) higher than 3%. Network capacity was then calculated in Erlangs per sector as being the maximum load in which BQC and BCR are lower then 5% and 2% respectively. Figure 2 presents Erlangs achieved when the users are using the AMR FR and HR channels without SAIC receivers for different bandwidth sizes and number of TRX, where the TRX number in the figure is related to the TRXs in the hopping layer, i.e. 2 TRXs means 1 BCCH TRX plus 2 TCH TRXs. The AMR FR simulations are limited by hardware, i.e., the bandwidth is increased, but the capacity remains unchanged. In real networks, the capacity will only increase by increasing the number of TRXs, or enabling some specific features that could increase the hardware capacity such as AMR HR or OSC. The AMR HR simulation curves reveal significant capacity gains mainly for environments with high frequency reuse and limited by hardware. For instance, in 10 MHz and 2 TRXs configuration the AMR HR capacity gain, when compared with AMR FR, is approximately 130%. The small gain observed in scenarios with low effective reuse is expected since those scenarios are limited by interference. It is important to remember that AMR HR channels are only used in good channel conditions in order to achieve a good speech quality. Additionally, Figure 2 shows that HR channel mode could be used as an efficient way for saving hardware resources. As it can be observed in this figure, by using HR it is possible to reduce TRX number from 6 to 3, and still have 13-14% capacity gain over FR channel mode. It is also possible to observe that for bandwidths bigger than 7 MHz, FR using 5 TRXs offers almost the same voice capacity of HR using 2 TRXs. In the examples shown above enabling the AMR HR, the spectrum is better used since more users can be allocated in the same amount of spectrum. Furthermore, some spectrum can be saved for the low frequency reuse scenarios. Since most of AMR HR curves presented in Figure 2 were limited by interference, a new set of AMR HR simulations enabling the SAIC receiver were done (Figure 3). It is possible to notice that with SAIC receiver, high AMR HR capacity gains are obtained even for small bandwidth cases and high number of TRXs, which are scenarios with low frequency reuse and, therefore, high interference level. The highest observed gains were for 5 MHz with 5 and 4 TRXs, with 167% and 155% gain respectively. Additionally, it can also be observed that the combination og AMR HR and SAIC receivers makes many scenarios to be limited by blocked calls. As an example it can be observed that scenarios with 6 and 5 TRXs have no difference in capacity for 7, 8.6 and 10MHz, which indicates that they are limited by hardware. This result shows that SAIC is very efficient to solve interference problems, thus can provide significant capacity gains in interference limited networks. Furthermore, it seems that the combination of AMR HR and SAIC receiver is an important step for re-farming of GSM networks since the network could operate in lower frequency reuse or a high interference scenario and, thus, allowing to release some GSM spectrum for another technology. As an example, if there is a network using 10 MHz and 6 TRXs, when using SAIC it can easily decrease the bandwidth to 7 MHz using 6 TRXs keeping the same voice capacity, or decrease it to 5 MHz with 5 TRXs and have only 20% reduction in voice capacity. As showed in previous results the AMR HR with SAIC receivers networks are blocked limited even for 6 TRX. Hence, the network capacity can not be increased by increasing the number of TRX. Nowadays, the operators intend to reduce the networks cost which means reducing, for example, the number of TRX. The OSC feature comes with idea of increasing the network capacity without need of increasing the number of TRX. The network capacity when the AMR HR, OSC (AMR DHR) and SAIC receivers are combined is shown in Figure 4. In all simulation cases using OSC it is possible to observe that when the bandwidth is increased also the the capacity is increased, while the number of TRXs remains the same. This means that networks became interference limited instead of blocking limited when deploying OSC. Maximum network capacity was obtained with AMR DHR, which has increased capacity by almost 30% in 10 MHz and 6 TRXs configuration. Additionally, an important advantage comes with AMR DHR, since it makes it possible to decrease the number of required TRXs for a given required load. Therefore, OSC implementation may bring cost savings in network implementation as well as in network operation, since when there is less TRXs it may be possible also to save energy. Figure 4 shows that a network with 7 MHz and 6 TRXs can save 1 TRXs using OSC, which will lead to a capacity increase of 7%, or it can use 4 OSC TRXs and experience a capacity loss of 13%. Besides, in 10 MHz configuration, 4 TRXs using OSC has the same capacity as 6 TRXs. For the 5 TRXs reference case, it is possible to observe that using OSC and saving 1 TRX, it is possible to have a 22% capacity gain with 10 MHz bandwidth. The results have shown that the combination between features for improving hardware efficiency, i.e. AMR HR and AMR DHR, and interference efficiency, i.e. SAIC, can really improve the spectrum and hardware usage which lead us to save spectrum and cost with radios. For 5 MHz bandwidth best results have shown 107% improvement over FR results without SAIC. Additionally, much more then the FR maximum achieved capacity of 44 erlangs, which is provided with at least 7 MHz, can be delivered with 5 MHz spectrum when OSC is used. In that case there is 66.2% gain of OSC with 5 MHz over FR with 7-10 MHz. These kind of results is crucial for operators which are planning re-farming in their networks. Finally, it is possible to determine some relationships between effective frequency reuse and gains obtained with the studied features as shown in Figure 5, were HR gain is comparison between AMR FR and AMR HR, SAIC gain is showing SAIC gains in over AMR HR, and OSC gain is presenting OSC gains over AMR HR with SAIC. It is possible to notice that features used for increasing hardware capacity such as HR and OSC have often small gains when effective frequency reuse is low. Both have shown small gains for reuse lower than 5, which can be explained since those features require high C/I ratios for keeping a good quality. On the other hand, SAIC has shown good results when effective reuse is low, i.e. in interference limited scenarios, although there were no gains in scenarios with high reuse. This is due to the fact that SAIC doesn’t improve hardware capacity, but is ...

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... it is possible to determine some relationships between effective frequency reuse and gains obtained with the studied features as shown in Figure 5, were HR gain is comparison between AMR FR and AMR HR, SAIC gain is showing SAIC gains in over AMR HR, and OSC gain is presenting OSC gains over AMR HR with SAIC. It is possible to notice that features used for increasing hardware capacity such as HR and OSC have often small gains when effective frequency reuse is low. ...