Wideband Code Division and Multiplication Access Souhaibe Barkat Communications Theory Final Project University of Colorado, Boulder, CO 80309 [email protected] Professor: Youjian Liu2Abstract When we talk about first generation systems we think about analog cellular systems. The second-generation systems are GSM (Global System for Mobile Communication), PDC (Personal Digital Cellular, 2nd generation system in Japan), cdmaOne (IS-95) and US-TDMA (IS-136). Third generation systems, which are designed for multimedia communication are to have high quality images and videos and to access higher data rate information and services on public and private networks. WCDMA technology has emerged as the most widely adopted third generation air interface. Introduction: The WCDMA specification has been created in 3GPP (the 3rd Generation Partnership Project), which is the joint standardization project from Europe, Japan, Korea, the USA and China. Within 3GPP, WCDMA is called UTRA (Universal Terrestrial Radio Access), FDD (Frequency Division Duplex) and TDD (Time Division Duplex), the name WCDMA being used to cover both FDD and TDD operation. Figure 1: WCDMA global market 1. Key Players: In the United States, the major users for WCDMA is Sprint communications and AT&T. However, Nokia and Erickson have just signed an agreement with Tmobile to upgrade to 3rd generation WCDMA from GSM. Qualcomm still makes chips for WCDMA, CDMA, and GSM, but it is pushing for older generations for upgrades to UMTS (Universal Mobile Telecommunication Serives) WCDMA. In Europe, Spirent Communications in Paris is a big user for WCDMA including many other companies. 90% of the cellular phone industry in Japan has already upgraded to 3-G WCDMA and working on upgrading to 4-G such as Wi-Fi, WiMax, and Wibro. Figure 2: WCDMA global growth 2. Frequency Band: Uplink: means that multiple users send signals to the base station Downlink or broadcast: Means that the base sends different signals to different users. In the United States Uplink Downlink Total WCDMA 1710-1770 2110-2170 2x60 MHz In Europe and Asia Uplink Downlink Total UMTS-FDD 1920-1980 2110-2170 2x60 MHz UMTS-TDD 1900-1920 2110-2025 20 +15 MHz 3. Standard Body: The work to develop third generation mobile systems started when the World Administrative Radio Conference (WARC) of the International Telecommunications Union (ITU), at its 1992 meeting identified the frequencies around 2GHz for 3rd generation mobile systems, both terrestrial3and satellite. Within the ITU these third generation systems are called International Mobile Telephony 2000 (IMT-2000). In North America, that spectrum has already been auctioned for operators using second-generation systems, and no new spectrum is available for IMT-2000. Thus, third generation services must be implemented within the existing bands. The WCDMA concept was formed around the WCDMA proposals from FRAMES/FMA2 (Future Radio Wideband Multiple Access System, EU research project), Jujitsu, NEC and Panasonic. Several European, Japanese and US companies contributed to the development of the WCDMA concept. The physical layer of the WCDMA uplink was adopted mainly from FRAMES/FMA2, while the downlink solution was modified following the principles of the other proposals made to the WCDMA concept group. 4. Modulation and Error Control Coding: Baseband Transmitter Architecture This section describes the digital architecture of a downlink transmitter that supports the W-CDMA standard. Figure 1 shows a block diagram of the transmitter. Blue blocks can be implemented in an Altera FPGA; orange blocks can be implemented in software in the Nios II embedded processor. Figure 3: Baseband Transmitter CRC = cyclic redundancy check DAC = digital to analog converter NCO = numerically controlled oscillator OVSF = orthogonal variable spreading factor RRC = root raised cosine To conform to the W-CDMA standard, cyclic redundancy check bits are added for error detection, and error correction bits are added for channel coding. The data is then spread with a user or channel-specific code to produce a DataStream at a given chip-rate. The spread data stream is scrambled with Gold code so that multipath signals can be uniquely identified and decoded by the receiver. To transmit a signal within the specified bandwidth, the data bits are shaped using a pulse-shaping filter. Next, the signal goes through carrier modulation and up-conversion to radio frequency (RF), and is then sent to the antenna to be transmitted over the air. A) Cyclic Redundancy Check The standard specifies four different polynomials for CRC checking: • gCRC24(D) = D24 + D23 + D6 + D5 + D + 1 • gCRC16(D) = D16 + D12 + D5 + 1 • gCRC12(D) = D12 + D11 + D3 + D2 + D +1 • gCRC8(D) = D8 + D7 + D4 + D3 + D + 1 Altera provides the CRC MegaCore® function, which can implement these polynomials and therefore meets the third-generation standard requirements. The CRC function is fully parameterized, including: • Variable length generator polynomial • Variable data width from 1 bit to the width of the polynomial • Any initial value B) Forward Error Correction The standard defines two encoding schemes to support different quality of services. For voice and MPEG4 applications, the standard employs convolutional encoding, which gives a bit error rate (BER) of up to 10-3. For data applications, the standard uses turbo encoding, which gives a BER of up to 10-6. Convolutional Encoder The required specification for a convolutional encoder is given below: • Base station: K = 9 and rate = 1/2 and 1/3 • Mobile: K = 9 and rate = 1/3 A convolutional encoder uses delay elements and XORs. Altera provides building blocks4optimized for Altera PLDs in the library of parameterized modules (LPM). You can use these functions, such as LPM_SHIFTREG and LPM_XOR, to implement a convolutional encoder. Turbo Encoder Turbo encoding gives a relatively large encoding gain with a reasonable computational complexity. This encoding scheme is useful for data services that permit longer transmission delays. The W-CDMA specifications are: • Parallel concatenated convolutional code (PCCC) with two 8-state constituent encoders and an interleaver • Block size: 40 to 5,114 bits • Puncturing: rate = 1/3 (no puncturing); rate = 1/2 (puncturing) Altera provides the Turbo Encoder MegaCore function, which