New scheme for CSFB improvement in LTE

摘要

Since Long Term Evolution (LTE) is a totally IP based cellular network hence, it only supports the packet switching (PS) function, which leads to the proposal of many alternatives for offering voice services over LTE to maintain the continuity of the most important cellular service over the new architecture of the celluar networks, these alternatives include Voice over LTE (VoLTE) which is the most cost and complexity ever for the voice service, also include the Circuit Switching FallBack (CSFB), the most widely deployed and currently exists alternative for voice service over LTE, meaning that it is the most preferable choice for many operators for its excellent circuit switching voice quality and SMS services delivering. The main drawback of the CSFB is the substantial call setup time delay, and if the worst fallback case happens, this time increased more, at this case the fallback happens at other MSC serving area than that MSC at which the registration was performed, therefore, at that case of fallback the Mobile Originating (MO) calls will need to perform inter-VLR location updating causing additional call setup time delay, on the other hand the Mobile Terminating (MT) calls will be dropped unless another functionality like Mobile Terminating Roaming Retry (MTRR) is adopted. This study is focused on the MTRR. MTRR is one of the 3GPP proposed solutions to solve the MT call dropping impact at MSCs boarders. Despite that MTRR found a satisfying solution for the problem of MT call dropping; on the other hand it made the call setup time nearly getting doubled. Therefore, it is important to analyze the fallback cases by giving a classification method for the fallback different cases, and the reasons cause that large additional call setup delay during CSFB. The paper also presents a new proposed sheme as an improved functionality to enhance the call setup time for both MT and MO calls during that case of fallback, caused by mismapping between Tracking Areas (TAs) and Location Areas (LAs) at MSCs serving area boarders, this new scheme with less procedures, reduces the call setup time for MT and MO calls at that case of fallback by finding a good method to perform the majority of the messages (causing that extra time) prior the MT/MO call procedures, and provide a solution for the limitations applied on MTRR, hence, improving the user quality of experience.