 which consists of 12 subcarriers (each subcarrier is 15 kHz). In DL, a OFDMA scheme is designed to allow signal generation by a 2048-point FFT. This enables scaling of system bandwidth to the needs of an operator. At least the bandwidths of {6, 12, 25, 50, 100} PRBs in the range of 1.4 MHz to 20 MHz are available, yielding a bandwidth efficiency of about 0.9. In DL, user data is carried by the downlink shared channel (DL-SCH), which is mapped to the physical downlink shared channel (PDSCH). The UL technology is based on Single-Carrier FDMA (SC-FDMA), which provides excellent performance facilitated by the intra-cell orthogonality in the frequency domain comparable to that of an OFDMA multicarrier transmission, while still preserving a single carrier waveform and hence the benefits of a lower Peak-to-Average Power Ratio (PAPR) than OFDMA. In the UL direction, user data is carried by the uplink shared channel (UL-SCH), which is mapped to the physical uplink shared chan- nel (PUSCH). With all the radio protocol layers and scheduling located in the eNB, an effi- cient allocation of resources to UEs with minimum latency and protocol overhead becomes possible. This is especially important for RT services such as VoIP, for which high capacity requirements were set: at least 200 users per cell should be supported for spectrum allocations up to 5 MHz, and at least 400 users for higher spectrum allocations [9]. © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization Properties and Requirements for VolP This section illustrates the characteristics of VoIP traffic by describing the proper- ties and functionality of the used voice codec in HSPA/LTE (Section 10.3.1) and by presenting the requirements and the used quality criteria for VoIP traffic in Sections 10.3.2 and 10.3.3, respectively. 10.3.1 Adaptive Multirate (AMR) Adaptive Multirate (AMR) is an audio data compression scheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP in October 1998 and is now widely used. The