Agilent Measurement Journal - Issue 4 - 2008 - (Page 20)

LTE objectives and timing The sidebar LTE at a glance (page 25) describes the major objectives of the LTE project and some of the key system attributes. Figure 1 shows an overall timeline for the LTE project. Compared to UMTS, the overall timescale is shorter, due largely to a much smoother standardization process. The development of LTE will avoid the 8000-plus change requests ultimately applied over a four-year period to the “frozen” UMTS Release 99 speciﬁcations. The instability and subsequent delays in the UMTS standard led to commercial deployment of a proprietary system in Japan before the worldwide standard was available. It is expected that the surprises and delays of UMTS will be averted with LTE, meaning its introduction should be more predictable and better able to avoid a proprietary launch. The dates in Figure 1 are acknowledged as aggressive and may slip; however, progress is solid and, as UMTS proved, trying to rush the process can be counterproductive. OFDM has been around since the mid 1960s and is now used in a number of non-cellular wireless systems such as Digital Video Broadcast (DVB), Digital Audio Broadcast (DAB), Asymmetric Digital Subscriber Line (ADSL) and some of the 802.11 family of Wi-Fi standards. In contrast, it has taken longer for OFDM to be adopted into cellular standards: It was brieﬂy evaluated in the late 1980s during the early stages of GSM and again a decade later as a candidate technology for UMTS but was not adopted in either case. The primary issue was the processing power needed to perform the fast Fourier transform (FFT) operations at the heart of OFDM. In the ’80s and ’90s, suitable processors were too expensive and power-hungry for mobile applications. Since then, Moore’s Law has come to the rescue for ﬁrst WiMAX then UMB and now LTE. Assessing the advantages of OFDM The primary advantage of OFDM is its resistance to the damaging effects of multipath delay spread (fading) in the radio channel. Without multipath protection, the symbols in the received signal can overlap in time, leading to inter-symbol interference (ISI). In OFDM systems designed for use in multipath environments, ISI can be avoided by inserting a guard period, known as the cyclic preﬁx (CP), between each transmitted data symbol. The CP is a copy of the end of the symbol inserted at the beginning. By sampling the received signal at the optimum time, the receiver can avoid all ISI caused by delay spread up to the length of the CP. OFDM: The choice of next-generation wireless With LTE joining UMB and WiMAX in choosing OFDM as the underlying modulation technology, it could be argued that there is now little to choose between these cellular systems. Of the ﬁve major new cellular systems, only HSPA+ and EDGE Evolution do not use OFDM, a difference clearly driven by the practical need for backwards compatibility with their respective installed bases. 2005 2006 2007 2008 2009 2010 Rel-7 Study phase Rel-8 Work phase Test specs Core specs drafted First test specs First First UE certification? commercial release Figure 1. LTE timing 20 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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