1: What are the characteristics of TDD technology?
L Time Division Duplex (TDD): distinguishes uplink and downlink based on different time slots
P advantages
N when the upstream and downstream services are asymmetrical, different quantities of time slots can be flexibly allocated to the upstream and downstream operations, resulting in high spectrum efficiency.
N uplink and downlink use the same frequency carrier, which facilitates the introduction of new technologies such as smart antennas and combined detection.
P disadvantages
N Implementation is complicated and requires GPS synchronization.
When N and CDMA technology are used together, it is difficult to control interference between upstream and downstream lines.
2: What are the characteristics of CDMA technology?
L strong anti-interference ability, high frequency reuse, and high spectrum utilization
L strong confidentiality: Signal similarity white noise after Spread Spectrum
L The user capacity of the system is soft, which has its own advantages and disadvantages
L high bandwidth usage: high requirements for power amplifiers (high power consumption)
L self-interference system-mutual interference between users in the system, difficult technical implementation
3: What is the voice encoding used by TD?
A: Amr (Adaptive multi-rate) has eight types of codes.
4: In the TD system, which code is used to differentiate users and communities?
A: differentiate users: Spread spectrum codes. The spread spectrum codes used by TD are OVSF codes.
L The uplink spread spectrum factor used by the TD-SCDMA is 1/2/4/8/16, with the behavior of 1 or 16
Differentiation of cells: scrambling code. The scrambling code used by TD is the gold sequence.
L The length of the scrambling code of the TD-SCDMA is fixed to 16 chips, a total of 128
5: What is the modulation method used by TD?
Answer: PSK, 16QAM (HSDPA)
6: What is the role of joint detection?
L reduces multi-path interference and multi-Address Interference to improve system capacity
L reduce noise increase and improve coverage
L overcome the far-reaching effect and reduce the power control requirements
7: what is the role of smart antennas?
L space isolation and interference elimination for users
P maximizes energy for expected users
P minimizes interference with other users
L The array antenna and the assignment algorithm can provide additional gain of more than 15 dB, thus:
P adds coverage to improve the signal receiving quality during buildings and high-speed motion
P improves the signal reception quality and reduces the disconnection rate
P increases system capacity
P reduces the transmit power and prolongs the battery life of the mobile device.
8: Common TD terms:
L bit: data that is encoded by the source and contains information.
L Symbol: Channel-encoded and intertwined data
L chip (Code chip): data obtained through final Spread Spectrum
L chip rate (CPS): Chip rate, basic parameters of CDMA System
P TD-SCDMA system code chip rate is 1.28 mcps
L spreading factor (SF, spread spectrum factor): the length of the Spread Spectrum Code
P symbol rate × Sf = Code chip rate
9: Advantages of the TD system:
L high spectrum utilization
P does not need to be paired with the spectrum. It can meet future expansion needs and bring great flexibility to spectrum allocation.
Compared with FDD operators, TDD operators have low spectrum acquisition costs and improve the spectral efficiency of voice and asymmetric data applications in terms of business.
L The TD system allocates asymmetric upstream and downstream transmission to support Internet access services economically and efficiently
L combined with smart antenna technology, it can provide fast and precise positioning services (LCS)
10: What is the unique business category of TD?
Session-based business: voice service and Videophone
Background services: data download, image Bell download, and email sending and receiving
Streaming Media Business: mobile TV, VOD, traffic monitoring
Interactive services: online games, Web browsing, and positioning services (LCS)
11: Design Philosophy of joint detection:
L perform "joint" processing on the multi-path components of signals of multiple users, making full use of user signal information such as Spread Spectrum Code, amplitude, timing, latency, etc., greatly reducing the multi-path and multi-access interference
Benefits of joint detection:
L reduce multi-access interference and multi-path interference to improve system capacity
L reduce noise increase and improve coverage
L overcome the unique "near-far effect" of CDMA and reduce the power control requirements
12: Design Philosophy of smart antennas:
L serious inter-cell user interference without Smart Antennas
L inter-cell user interference is greatly improved when smart antennas are used
Advantages of using smart antennas: see the above
13: Causes of TD uplink synchronization:
Basic concepts of uplink Synchronization
L uplink synchronization means that the uplink signals sent by users at different locations using the same time slot in the same cell reach the receiving antenna at the same time, that is, the signals of different users in the same time slot are synchronized when they reach the receiving antenna of the base station.
Reasons for using upstream synchronization:
L reduces uplink multi-access interference and multi-path interference among users in a cell, and increases the cell capacity and cell radius.
L make the TD-SCDMA has different from the CDMA 2000 and WCDMA patents, with independent intellectual property rights
14: The benefits of a system designed with the concept of SDR for network operation:
L devices of various communication systems share hardware platforms, saving data centers and reducing investment
L only software upgrade is required during technology evolution, and the construction of new technologies and standard networks is greatly accelerated
SDR Design Philosophy: use software (algorithms) as much as possible to implement RF hardware functions
15: What are the main QoS indicators of a service:
Link quality, cell capacity, and cell coverage
16: differences between open-loop and closed-loop power control:
L open-loop power control: Used in the initial access process
L closed-loop power control: used for business process
P upstream and downstream Inner Ring Power Control
P uplink and downlink Outer Ring Power Control
17: The difference between upstream inner ring and outer ring power control:
L uplink Inner Ring Power Control: NodeB controls ue transmit power
L uplink outer ring power control: RNC dynamically adjusts the sirtar to indirectly control the UE transmit power.
L downlink Inner Ring Power Control: ue controls the transmit power of NodeB
L downlink outer ring power control: ue indirectly controls the transmit power of NodeB by dynamically adjusting sirtar
18: hardware switchover, soft switchover, and Failover features:
L features of hard switching
P interrupts the link of the Source Community and then establishes the link of the target community.
P calls generate "gaps"
L soft switching features
P first establishes the target cell link, and then interrupts the source cell link to avoid "gaps" in calls"
The P-CDMA system is unique and can only occur between cells with the same frequency.
P soft switchover occupies more system resources than hard switchover
L advantages of failover
Compared with soft switchover, P occupies less system resources and increases system capacity.
Compared with hard switching, P has a short service interruption time and a low disconnection rate.
L Design Concept of failover
P uses the uplink synchronization technology to obtain the transmission time and power information of the switched Uplink Channel in advance during the switching measurement period, so as to reduce the switching time, the purpose of improving the switch success rate and reducing the switch-out rate
19: Glossary in the TD system:
P-CCPCH: main public control physical channel
Primary common control physical channel
RACH: Random Access Channel
Random Access Channel
Rscp: receive signal code power
Received signal code power
Prach: Physical Random Access Channel
Physical Random Access Channel
Fach: forward access channel
Forward access channel
Facch: Fast companion Control CHannel
Fast associated control Chanel
Fpach: fast physical access channel
Fast physical access channel
Dpcch: dedicated physical control channel
Dedicated physical control channel
Dpdch: dedicated physical data channel
Dtch: dedicated service channel
Dedicated traffic channel
Ccpch: public control physical channel
Common control physical channel
AGCH: access permitted Channel
Access grant Channel
S-CCPCH: Auxiliary-public control physical channel
Secondary common control physical channel
Usch: uplink shared channel
Uplink share channel
20: DCA (dynamic channel allocation)
Channels are centralized for centralized distribution.
Slow DCA: Allocate resources to cells
Fast DCA: Allocate resources to bearer services
21: N frequency point technology:
Configure N carrier frequencies per cell/sector, one of which is the primary carrier frequency, and the other is the secondary carrier frequency.
Carrier Frequency of P-CCPCH channel is the main carrier frequency;
Each cell/sector has only one primary carrier frequency. The upper and lower time slots occupied by the same UE are configured on the same carrier frequency.
Generally, public channels are configured at the primary carrier frequency;
Principles of the N-Frequency Technology in wireless planning: "The same frequency of the main carrier and auxiliary carrier"
22: HSDPA technology
Main technologies used: AMC and harq
Harq: Hybrid Automatic Resend Request, Hybrid Automatic Repeat request
AMC is mainly used for HS-DSCH (high speed downlink shared channel)
Harq is used in combination with ARQ and FEC, and FEC uses a turbo code of 1/3.
AMC provides rough and slow Adaptive Modulation for a large dynamic range;
Harq provides accurate and fast adaptive modulation in a small dynamic range;
23: Part of the TD-related signaling process:
Scenario 1: The UE initiates an RRC connection for registration. RNC decides to establish an RRC connection on the public channel and use the configured public channel resources without signaling interaction with NodeB.
Scenario 2: UE is the call to initiate an RRC connection. RNC decides to establish an RRC connection on a dedicated channel, and there is a signaling interaction with NodeB;
24: three channels added to the HSDPA physical layer:
HS-PDSCH: High-Speed physical downlink shared channel (downstream data)
A channel used to increase the data rate of a downstream link;
HS-SCCH: High-Speed shared control channel (downlink control signaling)
Downstream Channel carrying signaling information, each cell can have up to 32 HS-SCCH, each device can have up to 4 HS-SCCH
HS-SICH: High-Speed shared information channel (uplink control signaling)
25: Key technologies used by TD (6 in total)
Physical Layer: Smart Antenna, uplink synchronization, and joint detection
Network Layer: failover, DCA
High Level: TDD (Time Division Duplex)
26: HSDPA data transmission process:
HSDPA data transmission process:
The scheduling module in Node B evaluates different users and considers their channel conditions, the amount of data in each user's buffer zone, and the last service time.
After the user of the service is set, Node B determines the parameters of the HS-DSCH (downstream shared channel.
Node B First Transmits some necessary parameters to the HS-DSCH notification terminal before launching the HS-SCCH.
The terminal monitors the HS-SCCH, monitors whether there is information sent to itself, if there is, the terminal begins to receive the HS-PDSCH and cache it.
Based on information on the HS-SCCH, the terminal can determine whether the data received on the HS-PDSCH needs to be combined with the data in the soft buffer.
The terminal demodulation the data received on the HS-DSCH and sends a response ack/Nack on the upstream HS-SICH Based on the CRC results.
If node B receives the Nack, it resends the data until it receives the ACK message from the terminal or reaches the maximum retransmission count.
This article from the csdn blog, reproduced please indicate the source: http://blog.csdn.net/Eddy_0825/archive/2009/06/04/4243655.aspx
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