The legacy mobile wireless architecture shown on the right half of Figure 1 with a hierarchy of BS (Base Station)s, BSC (Base Station Controller)s, and MSC (Mobile Switching Center)s has a number of shortcomings with respect to handling of large volumes of data in B3G networks: i) wireless frame selection for handoff management is done at BSCs resulting in the duplicate traffic flow on the backhaul, ii) even during the ideal periods of a call, transmission resources are reserved resulting resources wastage in contrast to the IP-networks equipped with the statistical multiplexing scheme, iii) only 15% of the BS-BSC traffic is payload, and the rest is overhead, iv) BSs forward erroneous frames also BSC and this results in dead payload on the backhaul, v) uneven utilization of links makes the system inefficient, cost-ineffective, and unsuitable for deployment of new data intensive services, vi) transmission delays in long BS-BSC links could cause soft-handoff failures and call drops and thereby contribute to performance degradation, and vii) single-point failures of the legacy system entities or the links between them results in low system availability.
Figure 1: A novel distributed wireless router based RAN communicating with a legacy network (each pink dot represents a wireless router)
The demand for high quality services despite large volumes of call traffic necessitates a drastic reduction in the long backhaul (BS-MSC) control and data paths used in the legacy systems. An elegant approach to address the problem is to build the next generation RANs as distributed configurations of simple but functionally comprehensive wireless router (WR)s that could replace and at the same time inter-work, as shown in Figure 1, with the hierarchy of legacy wireless system entities i.e. the BSs, BSCs, and MSCs. Thus these new versatile WRs, need to have integrated into them several overlaying features of an all-IP 3G wireless network depicted in Figure 2. Even though the functional modules of the service layer are not detailed out in the figure in view of the ever growing number of wireless/wire-line services, typical entities that provide network services are call servers, bandwidth brokers, SLA (Service Level Agreement) managers, billing servers, HLR (Home Location Register)s, HSS (Home Subscriber Server)s, MGW (Media Gateway)s, SGW (Signaling Gateway)s, legacy servers, DNS (Domain Name Servers)s, and so on. The control layer supports the services with entities such as QOS (Quality of Service)/Mobility/Location/Power managers, Call Agents, and AAA (Authentication, Authorization, and Accounting) mangers. In the legacy systems, these two functional layers roughly correspond to the MSC and BSC functions, respectively. For execution of these functions, the legacy system entities (BSs, BSCs, and MSCs) need to communicate with one another. This is supported by backhaul IP networks with wire-line topologies. A part of the inter-BS communication is supported by wireless routing. Finally, the communication between the BSs at different cell sites and the mobile device constitutes the physical layer functionality of the wireless system.
Since the WR replaces the mobile network entities in the proposed RAN architecture, it needs to incorporate the control and routing functionalities of the legacy systems. In particular, it should have the following features: i) it should support all the data and signaling protocols for inter-router communication as well as communication with various service and control entities, ii) it should facilitate effective hand-off management to achieve nearly zero call drop rate, iii) it should provide high QOS by effective bandwidth management through traffic shaping, and iv) it should be capable of dynamically configuring its operational parameters in collaboration with its neighbors, and adapt itself to RF topology and other changes. Overall, it should render the RAN both high performing and highly available at a low cost.
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