01 WCDMA Principles HUAWEI TECHNOLOGIES CO , LTD www huawei com Huawei Confidential Internal Principles of the WCDMA System HUAWEI TECHNOLOGIES CO , LTD Page 2Huawei Confidential Preface � Now, the mo[.]
Internal Principles of the WCDMA System www.huawei.com HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Preface Now, the most popular term in the mobile communication field is WCDMA! What is WCDMA? And what is its benefit? Today, let’s go to know about WCDMA! HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Objectives After studying this course, you should be able to: Know the basic knowledge of the CDMA system Master advantages of the CDMA technology comparing with other multiple access technologies Know technical features of WCDMA FDD HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Contents Chapter WCDMA Principle Chapter Technical Features of WCDMA FDD HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Overview of CDMA Principles HUAWEI TECHNOLOGIES CO., LTD Radio Propagation Environment Multiple Access Technology and Duplex Technology CDMA Principles and Rake Receiver Huawei Confidential Page Multipath Environment Transmitted signal Strength of the received signal Time HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Fading Transmitted data Received data dB -5 -10 -15 -20 -25 -30 -35 -40 HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page Fading Rx power (dBm) Fast fading -20 Slow fading -40 -60 10 HUAWEI TECHNOLOGIES CO., LTD 20 Huawei Confidential Distance (m) 30 Page Frequency-Selective Fading P(f) P(f) Fading Narrowband Narrowband System System Transmit Signal f Received Signal P(f) f P(f) Fading Broadband Broadband System System f Transmit Signal HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Received Signal Page f Classification of Typical Radio Mobile Channels Static channel Pedestrian channel in typical urban areas (TU3) Vehicle mounted channel in typical urban areas (TU30) Vehicle mounted channel in rural areas (RA50) Vehicle mounted channel on the highway (HT120) HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 10 Scrambling in the WCDMA System Downlink: Different cells have different downlink scrambling codes Each cell is configured with a unique downlink scramble The UE identifies a cell based on the scramble The OVSF code is used to distinguish different users in a cell Uplink: Scrambles are used to distinguish different users In one cell, each user is configured with a unique uplink scrambling code The OVSF code is used to distinguish the services of a user Channel Source coding Interleaving coding and Spreading Scrambling Modulation interleaving HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 31 RF transmission Spreading and Scrambling Symbols xx sps 3.84Mcps 3.84M OVSF code Scrambling code 3.84Mcps HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 32 Chips after spreading and scrambling Code Generation Technologies in CDMA Random sequence (Bernoulli sequence) It consists of 0’s and 1’s only, with the number of 0’s equal to that of 1’s The probability of continuous or is as follows: 1/2 for one continuous or 1, 1/4 for two continuous or 1, 1/8 for three continuous or 1… One half of the shift sequence is the same as the original sequence and the other half is different m sequence - scrambling code used in the CDMA2000 system It is generated by the shift register As the longest linear shift register sequence, its period is 2n-1, where “n” stands for the length of the shift register When the delay is 0, the self-correlation function has a maximum value In other cases, the function value is always -1 It meets the Bernoulli sequence Its disadvantages are: Only one sequence is available and different users are distinguished by different phases So it has a high requirement for synchronization HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 33 Gold Sequence — Scrambling Code in the WCDMA System Gold sequence It consists of two preferred m sequences on the Exclusive-OR basis Its self-correlation function has multiple values, which is worse than the m sequence It exceeds the m sequence in quantity The Gold sequence is used to distinguish the cells and users in the WCDMA system owing to its good self correlation Good self correlation determines the Gold sequences can be used to distinguish users, thus the multiple access function is realized HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 34 Advantages and Disadvantages of the Gold Sequence Advantages: The Gold sequence needs no GPS synchronization and features high system flexibility and security The NodeB can work in asynchronous mode It is easy to realize indoor coverage Disadvantages: The Gold sequence has greater inter-code interference than the m sequence HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 35 Spreading/De-spreading Principle — Explanations for Frequency Domain Eb / No = Ec / Io × gain Power spectrum a2Tbit = Ebit Demodulation threshold Allowed maximum interference level of the system Gain Interference signals from other users HUAWEI TECHNOLOGIES CO., LTD Power that all the users can share Echip Huawei Confidential Page 36 Spectrum Change in CDMA Spreading code P(f) P(f) f P (f) Broadband signal f Narrowband signal f Noise Separation of signals and noise P (f) Signal combination Noise + broadband signal P (f) f Spreading code f The CDMA broadband spreading technology effectively avoids frequency-selective fading of radio channels HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 37 Rake Receiver Correlator Correlator Combiner Receive set The combined signal Correlator Calculate the time delay and signal strength Searcher correlator s(t) s(t) t t RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 38 Summary - Advantages of CDMA RAKE receiver is adopted The time diversity effect generated by channel coherence time is efficiently used Frequency diversity Wideband frequency spectrum Higher interference tolerance and security performance Low signal transmission power Great flexibility in carrying multiple services with largely different bit rate and QoS requirement Different spreading factors for different services with different data rates High spectral efficiency All users can share the same frequency spectrum simultaneously Supporting soft handover and softer handover HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 39 Contents Chapter WCDMA Principle Chapter Technical Features of WCDMA FDD HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 40 Characteristics of WCDMA FDD Channel bandwidth: 5MHz Chip rate: 3.84Mcps Frame length: 10ms Voice coding: AMR (Adaptive Multi-Rate) Uplink and downlink modulation: QPSK/QPSK Coherence demodulation aided with pilot Fast closed loop power control: 1500Hz Handover: soft/hard handover Support synchronous and asynchronous NodeB operation HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 41 Characteristics of WCDMA FDD Satisfy the minimum performance requirement of IMT2000 Compatible with GSM-MAP core network Comparatively steady version R99 has been released Support open loop and closed loop transmit diversity mode Support Common Packet Channel(CPCH) and Downlink Share Channel, adapt to Internet data access mode Support different fast power control algorithms and open loop, out loop power control Fully support UE locating services HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 42 Differences Between the WCDMA and GSM on the Air Interface WCDMA GSM Carrier spacing MHz 200 KHz Frequency reuse coefficient 1-18 Power control frequency 1500 Hz Hz or lower QoS control Through the RRM algorithm Through network planning (frequency planning) Frequency diversity The 3.84 MHz bandwidth enables Frequency hopping the air interface to use the rake receiver for multipath diversity Packet data Load-based packet scheduling Timeslot-based scheduling in GPRS Downlink transmit diversity Supported by the protocol to improve downlink capacity Not supported by the standard but can be applied HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 43 Conclusion This course describes the WCDMA system This course first describes some key technologies Then, describes the basic principles of CDMA and the WCDMA FDD mode After studying this course, we can have a preliminary understanding of WCDMA, thus laying a good foundation for subsequent study HUAWEI TECHNOLOGIES CO., LTD Huawei Confidential Page 44 Thank You ! www.huawei.com