Test & validation of next generation networks : WIMAX MAC layer in real time

Telecommunication Standards have been developing at a high pace following a frenetic curve. This has caused the manufacturers to urge the development of highly flexible, modular and scalable testing and verification methods for the production phase. The objectives have ranged from achieving cost optimizations addressing specific equipment domains, to methods based on virtual instrumentation opting multi-standard implementations. Exploiting the latter approach, it is possible to reuse the same hardware with the possibility of characterizing it using software extensions for the standard in question. Focusing solely on cost optimizations by having specialized test equipment has the limitations in terms of scalability, system flexibility and inability to adapt to other standards in the long term process. Even in situations where there exists the possibility of adaptation, significant redesigning of the architectures to accommodate multi-standard testing has been observed. For systems depending on virtual instrumentation, greater reuse of hardware and radio frequency resources is achieved; yet, there are limitations caused by the behavior of the Device Under Test (DUT) due to inherent off-line processing software which decouples the signal generation and analysis phase. The Software Defined Radio (SDR) paradigm has the undeniable advantage of off-line customization tools able to effectively reuse the same hardware with different personalized software. However, adopting the approach to complex standards like IEEE 802.16e (Mobile WiMAX) involve considerable concerns. The situation becomes more challenging when the DUT is multi-homed implementing several standards altogether in the same operative environment. In order to control the complexity, the test system is not only required to be flexible, scalable, adaptable and re-configurable, but also to be responsive. This, of course, entails that the system is able to process real-time full-duplex flow of information withstanding the timing constraints of the standard being dealt with. Production testing of Mobile WiMAX devices contrasts from conformance testing in a number of ways. It urges to verify the global behavior of the DUT after the integration of hardware and software components together. It is targeted on quality assurance of the production line by validating the operational characteristics of devices in real-time with simple and automated test cases. These test cases are formulated such that they are short, modular, fast and offer the possibility to be automated through compatible test applications. In this dissertation, it is desired to extend the functionality of the primary implementation of MAC layer for WisyMAX® Base Station Emulator (BSE), adapting it to suit the purpose of real-time production testing of Mobile WiMAX Subscriber Station (SS) devices. This task is intended to be executed by following the SDR paradigm, thus to develop the design and architecture in a way to make it reusable and adaptable for future upgrade in production standards. This is made possible by integrating virtualization techniques with reconfigurable hardware; thus, formulating and exploiting simple test suites This is done while stressing the simplification of the software using multiple layers of abstractions ensuring the software to be modular, fast, simple but effective; making it reusable for adaptation to other OFDM based standards (e.g. LTE, Wi-Fi). The whole idea is to exploit Virtual Instrumentation techniques by using reconfigurable, general purpose hardware and software. The work begins from an existing MAC layer implementation followed by its modularization, simplification and adaptation to suit real-time testing systems. The work progresses by cleaning the original source code, followed by its functional testing and reorganization. Moreover, documentation at both high and low level is developed for the system design, development and operation along with the proposal for a Multi-standard MAC. The novelty of our approach is to combine the SDR paradigm with those of Virtual Instrumentation, mapped on a Real-time environment in a way to concatenate the benefits of having re-configurable hardware and software with those of Real-time signal processing. The task involves selection and adaptation of the specifications of MAC layer from the WiMAX Standard, modifying them to support execution of modular and possibly automated sequences of test cases, followed by their development and deployment on a Real-time embedded hardware. The Real-time environment resolves the need of having specialized DUT testing software (e.g. in debug mode) or ancillary hardware (e.g. testing interfaces) during the final stages of production testing of SS devices. This allows for cost-efficient, transparent and reliable production testing of SS devices during final stages of production. Proven efficient method of Multi-site Testing can be employed by development of such a test solution, added with the advantage of possibility to reconfigure the system with minimal efforts. This can result in rapid parallel testing for device manufacturers to ensure quality conformance and validated operation of the produced units. The development of such a system will allow better evaluation of equipment capabilities of multi-vendor subscriber devices for 4G wireless. Production testing and certification efficiency are surely expected to increase with the realization of systems like WisyMAX-BSE®.