1, there are several multiple access methods? What's the difference between a variety of ways? There are three ways of multiple access, frequency division multiple access, TDMA, CDMA. Frequency division multiple access: a different business occupy different frequency channels, that is, to distinguish between different frequencies by different users. TDMA: traffic channel with the band occupied by different time slots, that is, through frequency + time slot to distinguish between different users. Code Division Multiple Access: a different business channels using different spreading code, that is, the user is on the same frequency by different spreading codes to distinguish the difference.
2, how to understand the global seamless 3G coverage? Because 3G is the 3G standard developed under the supervision of the Commission, and the unity of its band, so it can be seamless global coverage.
3, CDMA network is composed of those basic network elements? A mobile station MS, the base station BTS, base station controller BSC, the mobile switching center MSC, packet data controller PCF, Home Location Register HLR, Visitor Location Register VLR, such as packet data control node PSDN.
4, CDMA communication system model are those links?
Forward: source coding, channel coding, interleaving, scrambling, spread spectrum, modulation, launch. Reverse: reception, demodulation, despreading, descrambling, de-interlacing, channel decoding, source decoding.
5, how do you understand the bit, symbol, chip?
bit: Enter the data as containing bits of information. Symbols: After channel coding and interleaving of data after a symbol. Chip: After the final data obtained from a spread spectrum chip
6, CDMA systems use some of that code, their own role? Long Code: prior to the scrambling code used for encryption, the reverse used to distinguish different users. Codes: the former to the bias through different phases to distinguish between different sectors, both in the phase reverse to 0. Walsh code: forward for the spread spectrum, to distinguish between different users, the reverse for quadrature modulation to improve the reverse signal orthogonality.
7, CDMA system, walsh code resource is allocated? Pilot channel of the walsh code is 0, the synchronization channel walsh code is 32, paging channel of the walsh code is 1-7, and the rest for the traffic channel, if the paging channel walsh code 2-7 not allocated, the channel can also be used for business.
8, CDMA system, walsh code length is fixed it? In IS95 the, walsh code length is fixed 64-bit, in 2000, walsh code length is variable and the shortest is a maximum of up to 256 bits.
9, please describe the principle of Rake receiver? Rake receiver has a search engine, three related, search is used to improve the signal phase, the relevant phase via different signal demodulation, and then merge, effectively overcome by the decline of many to improve the receiver performance, and also the CDMA system, soft handover is possible.
10, CDMA channel code in several ways, for what business?
CDMA channel coding with convolutional codes and Turbo codes, convolutional codes is mainly used for voice service, Turbo codes as the coding efficiency is relatively high, but the delay is relatively large, mainly for data services.
11, briefly CDMA mobile station initialization process?
first CDMA frequency search, capture pilot channel, coherent demodulation to do, and then capture the synchronization channel, access to long code state, the system time, paging channel rate and other information to reach the paging channel, the receiving system parameters message, then into the parameters of the message, a list of neighborhood news, CDMA channel list messages, extended system parameters message, etc., and then waiting at the paging channel, doing registration, calling or paging response.
12, outlined the process of CDMA from the call? 13, outlining the process of CDMA soft-switch?
14, CDMA systems have those interfaces?
Um Interface: MS and the interface between BTS, carrying signaling and operational; Abis Interface: BSC and BTS interface between, carrying signaling and operational; A1 interface: between MSC-BSC signaling bearer; A2 interface: host MSC Inter-BSC operations; A3 Interface: SDU-BTS interfaces between, carrying signaling and user traffic; A7 interfaces: the source and target BSC signaling interface between the BSC; A8 interface: carrying business between BSC-PCF; A9 interface: carrying signaling between BSC-PCF; A10 interface: load the business between the PCF-PDSN; A11 interface: host signaling between the PCF-PDSN;
15, the mobile station under what circumstances trigger the registration, the registration for? There are nine cases, can trigger the registration process, the boot registration, off the registration, periodic registration, distance-based registration, the registration based on Zone, parameter change registration, the registration requirements should BSS, traffic channel registration, based on the User Zone Registration. The role of registration: report of the mobile station's location and status, type and version information, and work in the slot mode, waiting for the time slot information to facilitate the BSS system knows mobile station and paging communications to mobile units.
16, data services between the three states and three states is how to migrate? Three states: idle state, activated state, dormant state.
idle state to active state: the establishment of Um mouth, A1 interfaces, A8 interfaces, A10 interface. Active state to idle state: the release of Um mouth, A1 interfaces, A8 interfaces, A10 interface.
active state to dormant state: the release of Um mouth, A1 interfaces, A8 interface, retained A10 interface. Dormant to active state: the establishment of Um mouth, A1 interfaces, A8 interface. Sleep state to idle state: the release of A10 interface.
17, CDMA systems are those that channel?
IS95 channel are: forward: pilot channel, synchronization channel, paging channel, traffic channel, the first to add code division channel; reverse: access channel, traffic channel, reverse complementary code sub-channels.
CDMA2000 new channels are: Forward: Public power control channel, assignment channel public, public control channel, dedicated control channel, the first channel to the basic, forward supplemental channel
reverse: Anti-Wizard-frequency channel, the reverse enhanced access channel, common control channel, dedicated control channel, reverse fundamental channel, reverse supplemental channel.
18, the role of pilot channel? Use Walsh0 pilot channel spread spectrum, the base station transmit power value, the rate has 4800kbit / s and 9600kbit / s both to help the mobile capture system, multipath search, short PN code phase to provide information to help mobile phone channel estimation for coherent demodulation, switching phone pilot channel measurement, comparing the pilot strength.
19, synchronization channel effect? Walsh32 spread spectrum synchronization channel using the base station transmit power value, the rate for the 1200kbit / s, mobile phone access through the synchronization channel synchronization with the system to provide the system time SYS_TIME, long code state LC_STATE, paging channel rate, the basic network configuration parameters.
20, paging channel messages are issued to those systems? BTS broadcast channel public spending in the paging message, including: system parameter messages, access parameter message, a list of adjacent areas, CDMA channel lists, extended system parameter messages and so on. BTS paging channel paging through the phone and the traffic channel assignment.
21, power control purposes? Power control purposes: to reduce disturbance to overcome the distance effect. Not only improve the network quality of service
22, power control of classification? Reverse: Reverse open loop power control, reverse closed loop power control, reverse closed loop power control is divided into inner and outer ring. Forward: Report of the power control based on measurement (threshold and cycle), EIB power control, fast power control.
23, if the mobile station access was slow, and those parameters related? Mainly concerned with the access parameters, such as NOM_PWR, INIT_PWR, etc.
24, hard to switch to the types? Mobile phone supporting hard handover, pseudo pilot hard handoff, HANDDOWN hard handoff, direct hard-switching.
25, the mobile station has several search window, the general value to be? SRCH_WIN_A, used to search for the active set and candidate set pilots, generally set to 5,20 chip;
SRCH_WIN_N, to search neighboring pilot concentrated, generally set to 8,60 chip; SRCH_WIN_R, used to search for remaining focused on the pilot, the general set 9,80 chip
26, the current CDMA2000 carrier frequency can provide a number of channels to support the number of users?
current CDMA2000 to provide a carrier frequency of 40-45 channels to support 1200-1400 users. According to the specific value of the principles of capacity planning calculations.
27, a district of the call drop rate, should investigate the reasons for those aspects?
1, prior to the coverage problem. If you can not be demodulated forward link, mobile phone switched off the transmitter, thereby causing dropped calls. 2, the reverse link problem. FER performance for the reverse high. 3, pilot pollution. 4, the switching parameters is unreasonable. 5, the neighborhood relationship is unreasonable. 6, the search window to set unreasonable. 7, interference reasons. 8, the other issues. Others, such as the quality of transmission link, repeater, equipment failures, will lead to dropped calls, we need to link error rate of transmission, repeater selection and planning, attention to equipment reliability, etc., carry out regular maintenance checks.
28, soft-switching ratio is how to define, if the high proportion of soft handoff, how to scale down the soft switch?
the proportion of soft-switching = (CE traffic - Traffic Channel traffic (excluding switches)) / Traffic Channel traffic (excluding switches); cause abnormal ratio of soft handover of several key factors:
1, soft-switch with too much. With soft switching, ie the junction in the neighboring district planning regional band overlapping coverage, too often lead to soft-switch. From the drive test data, can grasp the situation with the soft switch. Mainly by adjusting the general height of the antenna, the next dip and azimuth control the size of soft handover zone, the method by adjusting the power setting to control the soft handoff zone requires careful attention to grasp the whole network structure.
2, no dominant frequency coverage. 3, the switching threshold set unreasonable. .
29, how to determine the pilot pollution? If a regional branch of the soft switching more and more than 3, although the soft handover branch or equal to three, but the candidate set also has a lot of pilots, and then Ec / Io is rather poor, this situation may exist pilot pollution.
30, what is fast fading, what is the slow rate of fall? Slow fading: the shadow effect caused by the obstruction, received signal strength decreases, but the field of geographical change in value with changes slowly, so called slow fading. Also known as shadow fading. Slow decline in the value of field strength lognormal distribution, and with the location / location-related; fast fading: synthesis wave amplitude and phase fluctuations with the movement of the mobile station has changed dramatically, as fast fading, the rate of decline depends on mobile station speed. Deep fading point distribution in space is similar to half a wavelength apart. Obey the Rayleigh distribution of its field, also known as Rayleigh fading, fading amplitude, phase, angle random.
fast fading can be further divided into the following three categories: time-selective fading: fast moving users in the frequency domain to generate frequency spread caused by the Doppler effect, which led to time-selective fading.
space selective fading: different locations, different characteristics of different transmission path fading. Frequency selective fading: Fading characteristics of different frequencies are different, causing delay spread, causing frequency selective fading. To reduce the fast fading effects of wireless communication, common methods of space diversity, frequency diversity, time diversity and so on.
31, what is an island effect, what is the tunnel effect?
island effect is caused because the base station coverage area covers more in areas distant from the base station form a small enclosed area, the mobile station is located in this region can not be cut and removed, causing a serious disturbance can easily cause mobile dropped calls. Tunneling effect is due to the terrain causes the formation of the tunnel effect, resulting in a long signal propagation, resulting in greater area coverage,
32, Okumura-Hata model for what the terrain to add, what band?
Okumura-Hata, macrocell prediction ,150-1500 MHz, from 1-20km; Cost231-Hata, for 1500-2000 MHz, macrocell prediction
Walfish-Ikegami, for 800-2000MHz urban, dense urban environment prediction; Keenan-Motley, for 800-2000MHz Indoor Environmental Prediction
33, Congestion Analysis: WALSH inadequate: WALSH less than in the voice business will not appear under normal traffic can only be great in traffic or application data traffic occurs. Value of 0525 corresponds to the release of the reasons (code resource allocation failure). Prior to the power shortage: the former may be due to insufficient power forward common channel take up too much power, the user is too large, set limits prior to the prospective entry caused by the irrational. Value of 0560 corresponds to the release of the reasons (forward restricted.) Reverse power shortage: the user may be excessive, the reverse quasi-entry caused by the irrational limit set. Reference prior to treatment. Value of 0561 corresponds to the release of the reasons (the reverse is limited). Channel inadequate: because the value corresponds to the release of 0562 (prior to the CE less than), 0563 (lack of reverse CE).
34, of failure of a soft switch, no dominant frequency coverage. 2, the switching thresholds and parameters unreasonable. 3, the drain with neighboring relations. 4, adjacent areas priority unreasonable. 5, the search window to set unreasonable. 6, before the reverse imbalance. 7, 8 congestion, interference
35, call setup failure analysis? 1, the network structure is irrational. 2, the power control parameter setting unreasonable. Forward traffic channel transmission power and initial traffic channel prior to the maximum transmit power setting is too small, may cause the mobile station can not correctly demodulate the forward traffic channel. Reverse power control process of the top post, there may be due before the reverse power control step size, frequency, Eb / Nt set parameters such as setting unreasonable cause the failure of the service channel demodulator. 3, access parameters, such as setting unreasonable NOM_PWR, INIT_PWR, PWR_STEP, RLGAIN_ADJ, RLGAIN_TRAF_PILOT and so on. 4, interference reasons. 5, pilot pollution. 6, message retransmissions set unreasonable. 7, before the reverse set unreasonable search window. 8, and switch the conflict. 9, the timer setting unreasonable
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