GSM principle

GSM principle

GSM is the abbreviation of Global System for Mobile CommunicaTIon. Means Global System for Mobile Communications. Divided into GSM900, DCS1800 and PCN1900 three frequency bands, the so-called dual-band mobile phone is the mobile phone that switches between GSM900 and DCS1800 frequency band. PCN1900 is a frequency band used by other countries (such as the United States). GSM900 / 1800 works in 890 ~ ​​960mhz / 1710 ~ 1880mhz frequency band respectively. The maximum power of the GSM900 mobile phone is 8W (in fact, the mobile station does not have such a large power, the general mobile phone has a maximum power of 2W, and the vehicle station has a large function), while the DCS1800 mobile phone has a maximum power of 1W.

l The difference between GSM900 / DCS1800 / PCN1900: GSM900 is the initial GSM system, the power output of MOBILE is 1W-8W, the channel of GSM900 is 1 ~ 124, the channel of DCS1800 is 512 ~ 885; DCS1800 is low power, the highest is 1W ;

l GSM frequency band: GSM900 cell with a radius of 35km, uplink 880 ~ 915MHZ, downlink 925 ~ 960MHZ

PHASE2: 890 ~ ​​925MHZ and 935 ~ 960MHZ; channel number 1 --- 124.

The radius of the GSM1800 cell is 2km (due to the low power of the 1800mhz mobile phone). Uplink 710 ~ 1785MHZ Downlink 1805 ~ 1880MHZ.

PHASE2: SAME; channel number: 512-885. For high-density users.

GSM1900: 1850 ~ 1910MHZ 1930 ~ 1990MHZ

The uplink and downlink form a frequency pair, the uplink is the mobile phone transmitting and the station receiving; the downlink is the base station to the mobile phone. For example, the difference between 935-960 and 890-915 is 45MHZ. On the second channel, the upstream channel lags the downstream channel by three time slots.

Network composition:

1. BTS base station: base transceiver staTIon The base station is mainly a transceiver. The number of transceivers determines the capacity of the cell. One transceiver can support 8 users. A cell consists of 3 antennas, one transmit, and two receive (hierarchical receive). (

a) Each BTS will have a set of transceivers.

b) A BTS covers a cell, and the BTS sends BCH signals in time slot 0 of the RF channel. BCH helps Mobile identify / find the network.

c) The cell phone user capacity of the cell depends on the number of channels

d) The data transmission rate of the GSM air interface is 13Kbps, that is, the BTS voice data transmission rate is 13KB / S.

e) There is a BTS instructing the mobile phone to set its transmission power, timing, and switching.

2. BSC base staTIon controller:

a) Several BTS base stations are connected to one BSC, the base station arranges channel configuration, handover, and BTS to connect to BSC; all BSCs are connected to MSC,

b) Each BTS is connected to BSC with an abis interface, which is a 2Mbps connection. Use microwave link, opTIcal fiber, co-axial line and other methods to connect.

c) Microwave link is often the best choice of connection.

d) BSC connects to MSC using port A

e) BSC can provide cell broadcasting and other services.

3. MSC mobile switching center is the core of the network, call establishment, hold, and release; link BSC and PSTN, authentication, call transfer, short message, charging, etc. When the number of users increases to a certain number, MSC can be added; GMSC is used between MSC and MSC (GATEWAY)

a) When the call is established, the MSC functions to maintain the call and disconnect the call.

b) Store all user data and their related characteristics.

c) Between MS and PSTN, exchange communication data.

d) MSC is the heart of GSM network. It is a connection port with other GSM networks and non-GSM networks.

e) MSC main functions: authentication, location update, connection, charging, call transfer, SMS.

f) When the number of users increases and the capacity of one MSC is exceeded, one more MSC is needed, and the number of users doubles

4. TRAN ------ Trans coding / rate adapter unit rate adapter.

a) TRAN converts the GSM rate of 13KB / S to the standard 64KB / S; TRAN is part of an MSC.

b) Trans coding is also used in the downlink to convert 64kbps to 16kbps.

c) Trans coding is in MSC \ BSC \ BTS.

5. HLR Home location register.

a) All user data inventory in MSC resides in HLR. There is a permanent user database in HLR.

b) When a user makes a call, the MSC obtains user data from the HLR. It is the user's core database, and most of the data in the SIM card can be obtained in the HLR.

6. VLR visiting location register.

a) There are all subscriber numbers activated in the VLR.

b) When a user in another MSC roams to a new MSC, the MSC communicates with the HLR, and the new MSC registers the roaming user in its VLR.

c) When the mobile phone roams, the user access area is covered by another network, and the home location network approves it to use the visited network, its user information will be copied from the HLR to the VLR (visit location register) for temporary storage.

7. Authentication center AUC ---- Authentication center

a) is the SIM card verification process.

b) Each SIM card has an IMSI, and a password is added to the IMSI

c) IMSI and password in HLR

d) When communicating with a mobile phone, first verify the legality of the SIM card, which is verified by the AUC.

8. Equipment identity registration: EIR ---- Equipment identify register

a) Contains IMEI information. All mobile phone IMEI are stored in EIR, which is the mobile phone database.

b) In GSM, it helps to verify that when the phone is lost, the operator can prohibit the use of the phone that has been reported as lost.

c) EIR classification: Permitted list \ evaluation list \ stolen list \ unknown

9. Toll Center BC --- Billing center

a) BC generates the cost status of each user.

b) Connect directly to MSC, and MSC will send charging information to BC (during conversation)

c) BC processing is billed per unit.

10. Operation and operation center: OMC ---- operation and maintenance center.

a) Each GSM network consists of more than 100 BTSs, and each entity requires operation and maintenance.

b) Some remote manipulation is necessary, detection and remote entry.

c) Sometimes there are two kinds of OMC (different suppliers), OMC-S: Deal with switch; OMC-R: deal with radio network.

11. Short message center: SMSC information is sent to the designated mobile phone through the short message center.

a) Information is transmitted via SMSC

b) Information can be sent through manual terminals (connected to SMSC).

c) SMS CENTER --- MSC / VLR ---- BSC ---- BTS .---- MS

12. Voice Service Center:

a) It has a database of all voice users;

b) It also stores voice messages.

13. Equipment alarm:

a) BTS, BSC, Trans coder failure.

b) Link failure

c) Module failure (transceiver, processor)

l Cell identity, each cell in the network has a unique identification number, CI: Cell Identity. A cell can be used by 56 users to talk at the same time

l Modulation method: GSM uses 0.3GMSK modulation Gaussian minimum frequency shift keying, 0.3 is to describe the relationship between filter bandwidth and bit rate, not phase modulation, it is a typical digital FM modulation, in fact, FM. 0 and 1 represent different frequencies of carrier addition and subtraction + 67.708KHZ and -67.708KHZ, 1 is regarded as a phase increase of 90 degrees, 0 is regarded as a phase change in the opposite direction, two frequencies represent frequency shift keying; The speech coding rate is 13kbps. The data rate (modulation rate) BIT transfer rate is 270.833Kbps. It is exactly four times the RF frequency shift. In this way, the modulation spectrum is effectively reduced and the channel utilization is improved. Gaussian filtering: dramatic frequency changes will cause spectrum dispersion, so after filtering with a filter, the spectrum dispersion is reduced; the RF carrier frequency is increased by 67.708 and 67.708KHZ ; Transfer by frequency.

l GSM network system: The interface between the mobile phone and the station is an air interface, and the base station (BS) and the base station console BSC are connected by abis interface 2Mbps. (It is an optical fiber or a commonly used microwave connection. The DCS1800 Abis interface often uses a microwave connection). One BSC controls 20 to 30 BTSs; the base station console BSC is connected to the switching office through the A port. The maximum distance between the mobile phone and the base station is 34.9km.

Steps after the phone is turned on:

1. First search 124 channels, that is, all BCH channels, determine the BCH strength of the received broadcast channel, (the information carried by BCH is the BTS closest to Mobile; call information);

2. Synchronize time and frequency with the network, adjust frequency and time by FCH / SCH

3. Decode the BCH sub-channel BCCH.

4. The network checks the legal identity of the SIM card. Whether it is a SIM card allowed by the network.

5. The location of the phone is updated.

6. Network authentication

l Mobile calling (MOC) process:

1. The mobile phone sends a channel request to the base station, that is, the mobile phone sends a short random access burst. (RACH Burst)

2. The transmission channel is designated by BCH. SDCCH

3. The mobile phone and the base station communicate on an independent dedicated channel (SDCCH).

4. Authority authentication

5. Specify the mobile phone to communicate on a traffic channel (TCH).

6. Voice communication on TCH.

Cell phone called

1. BTS uses the IMSI number in the SIM to call the user on the PCH call channel.

2. Send RACH from mobile phone

3. The channel is specified on BCH.

4. Mobile phone and base station communicate on SDCCH

5. Mobile phone users are authenticated

6. The mobile phone is assigned to the TCH channel.

7. Carry out voice and data communication on the TCH channel.

Emergency call:

1. The GSM specification defines 112 as the emergency call number

2. 112 can be called with or without a SIM card.

3. On RACH, mobile phone 112 establishes an emergency call.

l Authentication:

1. Purpose: to verify the user's identity (IMSI / SIM); to provide a new encryption key for the mobile phone.

2. Under what circumstances is authentication: every registration, every call or called attempt, perform some value-added services, location updates when roaming.

l Handover: Handover is the mobile phone communication from one cell / channel to another cell / channel.

1. Upstream and downstream reception quality reports

2. Upstream and downstream received signal strength

3. Distance, time

4. Interference layer.

5. Power budget.

6. Switching includes: switching between internal channels / slots in the same cell. Cells are between cells.

l Encryption ciphering: the confidentiality of voice and data, and the confidentiality of signal information;

l Phone location update: location update:

1. The MSC should know the location of the calling mobile phone.

2. The mobile phone continuously changes the location. When the mobile phone changes the location, it informs the MSC about the new location. The location update is handled by the MSC.

3. Mobile phone location update process: (location area identity LAI)

a) Mobile phone changing location area

b) The mobile phone reads the new location area from BCCH

c) Send RACH, which is the channel requirement.

d) Get an SDCCH on AGCH.

e) Send IMSI and new and old LAI location update requirements to MSC on SDCCH

f) MSC begins certification

g) If the authentication is successful, update the phone location on the VLR

h) Send confirmation message to mobile phone

i) The phone leaves SDCCH and enters idle mode.

l Uplink and Downlink: Uplink is that the mobile phone sends information to the base station through the uplink frequency, and downlink is the opposite. Upstream and downstream form a pair of frequency pairs (45MHZ division), upstream lags downstream three slots; upstream and downstream use the same slot number; upstream and downstream use the same channel number; upstream and downstream use different bands. (Interval 45MHZ).

Power level:

Because the mobile phone moves in the cell, its transmission power must move with it. When he is close to the base station, the power to prevent interference to other users should be reduced. When he is away from the base station, the transmission power should be increased to prevent attenuation. There are 19 power levels in total, and the power levels are stored in the EEPROM of the mobile phone. The advantage of power control is that the mobile phone can save power and the base station can reduce interference.

1. The base station sends a command on the SACCH to change the transmit power of the mobile phone

2. Changing the power is proportional to the attenuation of the path. TX Level 5 –33dbm, 19 --- 5dbm.

3. The interval between each level is 2dbm.

4. BTS needs Rxlev and Rxqual starting on the upstream

5. Send report to BSC about Rxlev and Rxqual every 480ms.

6. Compare with the initial one every certain time.

Dynamic base station power control:

1. The goal is to reduce the average interference

2. Calculation based on measurement report sent by MS

3. Not with BCH carrier? ? ? ? .

4. Not mandatory

DTX discontinuous transmission:

1. When the voice is interrupted for most of the time, allow the wireless transmitter to turn off.

2. There is a DTX Handler processor: there is voice activation detection at the transmitter, background sound noise at the transmitter, and comfortable noise when it is cut off.

3. Discontinuous transmission is performed on both upstream and downstream. Discontinuous transmission, discontinuous reception;

4. Perform discontinuous transmission and discontinuous reception on the mobile phone.

5. There is discontinuous reception during BTS reception

Time shift (time advance):

Timing advance is to ensure that the signal can reach the BS in an accurate time. When the MS moves, as the distance between the MS and the BS, the delay of uplink transmission is variable, the base station orders the mobile station to send in advance. The BS commands the MS on the SACCH channel to change its transition size. The receiver station decodes the BCH when the mobile phone is in idle mode. The SCH in the BCH allows the mobile phone to adjust its internal time. How far away from the base station, through SACH special short burst. When the mobile phone obtains the time-shifting information on the downstream SACCH, the normal burst is sent, and the 30KM mobile phone is set to delay 100US.

Channel introduction:

1. BCH broadcast channel:

BCH is like a lighthouse. At any time in every cell, there is BCH on ARFCN, so that the mobile phone can discover the network and synchronize the mobile phone with the network, and the strength of the BCH signal tells the mobile phone that it is the closest GSM network; Almost every 30 seconds, the BCH power of the neighboring cell will be reported so that the base station can decide whether to switch. The BCH frequency channel used by each cell is different, and the channel is repeatedly used by the cell at a long distance; all mobile phones in the cell receive BCH. There is a BCH channel on the ARFCN. The BCH information is on the downstream channel 0, and the other time is used for service information TCH; to synchronize the MS, carrying control information and call information. And network identity information. The call information of all mobile phones is on the BCH. BCH consists of FCH, SCH, BCCH, CCCH, SDCCH, and SACCH. The BCH generated by the base station is in the zero time slot,

a) FCH: frequency correction channel reuses special BURST on BCH to allow the phone to adjust its frequency when it is turned on.

b) SCH: synchronization channel, after FCH, adjust the time.

c) BCCH: Broadcast control channel, with network identity.

d) CCCH: shared control channel, its sub-channel PCH (PAGING CHANNEL) is on CCCH. The mobile phone can recognize and respond with a RACH. There is also a sub-channel AGCH to access the approved channel and order the mobile phone to enter SDCCH or TCH.

2. CCCH shared control channel: is a bidirectional control channel, CCCH and BCH share 0 time slots on multiple frames; CCCH includes RACH; PCH; AGCH; CBCH; PCH call channel is used to carry IMSI to report that the mobile phone has a call, PCH is downstream aisle,

3. DCCH dedicated control channel: Bidirectional control channel, composed of three sub-channels: SDCCH, FACCH, SACCH.

u SDCCH independent dedicated control channel: specify the transition channel before TCH, traffic establishment and user authentication. SDCCH independent dedicated control channel: play a connection role between BCH and TCH during call establishment

u SACCH slow related control channel:

Uplink: Received signal quality report, received signal RX LEVEL report, BCH power report of neighboring cells. Channel power; status of the phone.

Downlink: commands for the TX power control of the MS, cell channel configuration, time shift, and frequency hopping.

u FACCH fast related control channel: used by BTS to command mobile phone switching,

Upstream: Interrupt TCH signal, fast information exchange when switching.

Downstream: Interrupt TCH. Control BITS

u The difference between SACCH and FACCH: SACCH reports that the base station says that there are additional cells to provide better signal quality to the mobile phone, and handover is necessary. During a period of time, SACCH does not have enough bandwidth, so it is replaced by FACCH in a short time TCH; Switchover occurs. FACCH is like a TCH. When you hear a small interruption in the voice, the switchover may have occurred.

4. TCH business channel: the channel used during the call. Carrying voice information, is a two-way for mobile phones and base stations to exchange voice information, TCH full rate 26 frames is 120ms. Contains 24carry speech, 1 idle, 1 sacch. TCH half rate 26 frames is 120ms; contains 24carry speech, 2 sacch.

5. RACH random access channel:

The mobile phone sends a short burst to the base station, that is, the call demand; it is used by the MS to get attention from the base station; the mobile phone does not know the delay of the path, so the mobile phone sends a short BURST, when the mobile phone gets a transition on the downlink RACH, the mobile phone Only normal BURST is sent.

6. Mobile measurement report:

The SACCH measurement report is provided to the GSM system. Each mobile phone measures the power of the serving cell and the BCH power of the neighboring cell; the mobile phone also measures the strength and quality of the signal received on the TCH. Report the received RxLev (dbm) and RXQuaL (be mapped directly to bit error ratio) to the serving cell through SACCH.

7. Reception performance: The GSM receiver must operate effectively in a complex infinite environment. The receiver should adapt to multipath and Doppler attenuation, low signal, high signal, and interference from other receivers or other users. It is necessary to be able to demodulate the 0.3GMSK signal with the smallest bit error rate. The voice information of the GSM voice channel is encoded as Ia and Ib with error correction, while IIbits has no error correction. The intermodulation test of the mobile phone's choice of two interferences in the GSM band,

l IMEI is the international mobile equipment identity. The international mobile equipment identity is the serial number of the mobile phone. Each mobile phone has a unique serial number that is different from other mobile phones. IMSI: international mobile subscriber identity The international mobile subscriber identity is the correct identity of the mobile phone user to enter the network. The 15-bit IMSI is stored in the SIM card.

l SIM subscriber identity module: 4-8 digits PIN code, 3 times wrong input card will stop working; 8 digits PUK code, 10 times wrong input SIM card will be locked permanently. The SIM card contains: serial number, IMSI, authentication algorithm encryption, network code, PIN PUK, charging information. SIM card: keep all user information, (IMSI \ allowed network list); store the last location information. Dial information and store information. Store phone number, etc.

l Dual band & dual mode:

1. dual band: Dual band, mobile phone has frequency switch, can work in two frequency bands

2. dual mode In mobile phones, mode is the type of transmission technology used, digital mode and analog mode. The mobile phone supports AMPS and TDMA, which can be converted as required. AMPS is simulated.

l Mobile Station ISDN number: (MSISDN): Mobile phone number.

l Community access technology:

1. FDMA: frequency division multiple access: Each call is placed on a separate frequency.

2. TDMA: Time division multiple access: On the specified frequency, the call is on a fixed time period.

3. CDMA: Code division multiple access Each call has a unique code.

Time division multiple access technology:

1. GSM uses TDMA and FDMA multiplex transmission: 124 Frequency channels for GSM900; 100khz channel; mobile share ARFCN by TDMA. 0.3GMSK Modulation 270.833kbits / sec.

2. There are 124 channels in the GSM system, and the channel interval is 200khz; each channel is shared by 8 users and time-division multiplexed in time. That is to say, the signal is sent in bursts instead of continuously. The upstream and downstream regulations use the same channel number (ARFCN) and time system number, and the base station and the mobile station differ by three time systems, that is, the upstream circuit lags the downstream circuit by three time systems.

Physical and logical channels:

Physical channel: It is described in the time domain and frequency domain; it is the actual frequency and time domain, which is determined by the channel or absolute radio frequency channel number and time system. The combination of TS number and ARFCN is the physical channel.

Logical channel; is on the physical channel, and may be a business channel or a control channel at any frequency and time.

l 1 timeslot period = 576.92us, 1frame = 8timeslots. Frame period = 4.615ms, voice coder bit rate = 13kbps,

l In Timeslot / normal burst, there are 26 bits of slow or training bits.

l Hopping service channel: All mobile phones have the ability to hop frequencies, but not all cells are hopping areas (like cities with many buildings causing multipath, which are set as hopping cells). The mobile phone measures the strength of the adjacent cell bch, and the hopping order is defined by the cell configuration and the mobile phone configuration table. The cell configuration table lists all special cell hopping sequences.

1. Cell reselection ----- Measure and perform BCCH decoding: MS calculates serving cell C1 and non-serving cell C2 every 5 seconds

2. The MS must decode all BCH data of the serving cell at least every 30 seconds.

3. Mobile phone decoding BCCH data contains parameters that affect cell selection. At least 5 minutes, the 6 strongest cell BCCH carriers.

4. When the MS finds the 6 strongest BCCH carriers, the BCCH data arrives at the new carrier within 30 seconds.

l Frequency hopping:

1. Multipath attenuation produces different signal strengths called Rayleigh attenuation

2. Rayleigh attenuation is determined by different paths and the resulting receiving frequency

3. A fast-moving mobile phone may not experience dramatic effects due to changes in the path? ?

4. Slow or stopped mobile phones may experience a serious impact on voice quality (why)?

5. If the frequency change is accepted when attenuation occurs, the problem will be solved

6. The attenuation phenomenon is continuous and fast, so the frequency change should also be continuous.

7. This continuously changing frequency is called frequency hopping

8. Perform frequency hopping on both upstream and downstream

9. The frequency of each TDMA frame changes

10. The phone's frequency hopping up to 64 frequencies

11. Is the jumping sequence cyclic or acyclic? ? .

12. What is the frequency hopping sequence? ? Different frequency hopping sequences can be used in the same cell.

13. Does BCH time slot skip? ?

14. Frequency hopping can reduce the average interference. Even if the common channel cell will use the same ARFCN frequency hopping, the interference will be discontinuous.

15. GSM cell is not frame synchronization, the frequency change is related to Frame nos.?

16. If the same HSN (??) is used in two cells, the interference will either be zero, or will it be continuous if a phase correction exists? ? ? ?

17. So the two cells should use different HSN as much as possible.

18. The fan-shaped cell (same BTS) can use the same HSN, because the area does not appear at the same time.

l Voice coding: Voice compression technology is used in modern digital communications, RELP residual excitation linear precoding and LTP long-term and coding. Voice quality is affected by the primary Ia bits, with error detection plus CRC error correction. Evaluation of voice quality MOS = Mean opinion score, 1 --- 5; 5 is the best. 1 is the worst.

GSM cellular communication system and measurement

The first band of analog mobile communication technology: it is an analog system, and the information on the channel is transmitted by analog voice information, and analog modulation (frequency modulation) is used. There are shortcomings such as spectrum utilization, capacity, power utilization, and confidentiality.

The second generation of digital, narrow-band mobile communication technology based on telephone services. The voice compression coding is used to digitize the voice and modulate with multiple coding methods of TDMA and FDMA.

The third-generation broadband mobile communication technology with limited multimedia services. It is a global personal mobile communication system, providing 2Mbps data stream for users who are stationary or slow moving, and 144Kbps for high-speed moving users. The medium speed is 384Kbps. There are several standards: WCDMA; CDMA2000.

The fourth generation is a broadband mobile communication technology for multimedia purposes.

l Instruments used in GSM measurement:

Time domain analysis: oscilloscope is easy to observe phase distortion.

Frequency domain analysis: Spectrum analyzer is easy to observe harmonic distortion.

Encryption cipher / encryption: Security is a characteristic of the GSM system, the encryption switch is controlled by the base station,

The principle when measuring is:

There must be enough power to ensure the connection, connect the modulation quality, and overcome the attenuation of the path; the selected measurement: to avoid false and bad, find out all the true and bad, and explain the failure; why is the measurement required when measuring? And what to look for? Provide reliable quality, reliable operation safety, and provide defective data to manufacturers. Look for potential production defects, defects in the production process, and results from the life of the mobile phone and damage. Peripherals to be tested in actual production: keyboard and display, battery connection, SIM card connection, headset voice, antenna test, LCD display, etc.

1. Bit error rate:

The performance of the receiving sensitivity, BER bit error ratio is to evaluate the reception at the time of analog input. All mobile phones have a LOOP BACK mode, and the GSM TEST SET sends commands to the mobile phone to put the mobile phone into Loop back mode, and only When TESTSIM is inserted into the mobile phone, loop back can be activated. Once the mobile phone loops back to the modulated data stream, BER can be measured; bit errors are caused by mobile phone reception. A base station is simulated by GSM TEST SET and generated by GSM TEST SET A high-quality 0.3GMSK signal is used to establish a call with the mobile phone. The mobile phone is commanded to enter the loop back mode. Usually the voice data is encoded on the TCH, but this time it is replaced by a pseudo random binary sequence and the PRBS is modulated in the downlink. On the TCH of the mobile phone, the mobile phone receives and demodulates the PRBS and remodulates it to the upstream TCH. In the TEST SET, the demodulation and comparison with the original PRBS. The error is in percentage.

2. Receive static sensitivity:

The mobile phone moves in the cell. Due to the attenuation of the path, the base station uses RXLev sent from the mobile phone to display the received power. When the received power is small, the base station adjusts its output power; this is called dynamic power control, and the range exceeds 30DB. BER <2% at the farthest -102dbm, BER <0.1% at the highest (closest) -15DBM;

a) Receiving sensitivity under decay conditions.

b) Reception performance under interference conditions:

3. GSM BURST:

It is the power versus time. The flat part of the 0.3GMSK burst is a useful part, and its fluctuation range should be within ± 1.0dbm. Power versus time burst profile: use time gate spectrum analyzer, set the zero frequency span (SPAN) by the spectrum analyzer; adjust to the signal center frequency, the resolution bandwidth should be selected to be narrow enough so that the signal-to-noise ratio can display the entire Burst's dynamic range, and resolution bandwidth should be sufficient not to distort the outline of the display.

4. Measure the output RF spectrum:

The average trajectory of the RF modulation output spectrum is dbc compared to the average value of the center frequency. Because of the RF spectrum output by Ramping. The measurement of the Ramping spectrum is to protect users who use adjacent frequency channels, and requires TDMA burst to have sufficient dynamic Range, rise fast enough, do not exceed the target, and be flat in the center. The appearance of ripples in the center of the burst is desired for product measurement. The instantaneous input frequency is close to ± 67khz and the data model? ?

5. Test for the emission of spurious waves:

1. Protect other wireless spectrum users from interference. To test in R & D, production is generally not required.

2. Protect other users from 9KHZ to 12.75GHZ. , Idle mode / calling

a) Use the Spectrum analyzer to search all spectrums within 9K-12.75GHZ.

b) In idle mode and in talk mode.

c) Under the completely shielded RF measurement conditions, the other infinite spectrum should be shielded.

6. Launch part:

The EEPROM stores the I / O gain balance parameters and the shape parameters of the Ramping control circuit; the calibration power value and power correction coefficient of the transmission output are also stored in the EEPROM; the transmission output power is the most important protocol in the GSM regulations. All collections require an EEPROM calibration table to meet the requirements of the GSM protocol. At different output frequencies, the power calibration table leaves a correction value for each power level; the transmit output power can be measured by GSM TEST SET. The maximum power output deviation is 2dbm. Others are 3dbm. Deviation.

7. Modulation and synthesis is to convert the data stream from the channel encoder to the wireless signal, modulation and channel synthesizer into a single line. ?

8. Phase and frequency errors: Phase and frequency errors can show many performances of mobile phones. Peak phase error peak <20deg; average phase error <5deg; frequency error <90hz.

9. Time base adjustment range

timing tuning range: The time base adjustment range check is done by each mobile phone manufacturer. All mobile phones have an internal frequency reference oscillator (time base), and all other frequencies in the mobile phone must be synchronized with this reference frequency; this The reference frequency is adjustable, so the phone can be synchronized with the network; sufficient adjustment range is necessary. It is because of Doppler attenuation and temperature changes.

10. dbc measures the radio frequency spectrum. The spectrum curve measurement caused by modulation compares the average measurement result with the average value at the center frequency, which is the relative dbc value.

11. RELP: Residual excitation linear precoding. LTP: Long-term precoding.

12. Idle mode: I am not on a call, but still camp on the network. Receive and decode BCH from the base station.

Camp on:

Preferred list.

QUSTION:

1. How many antennas does a base station in a cell usually have? 3
2. Can an antenna transmit several channels at the same time? If not, how to provide several channels to a community at the same time?
3. Can a control channel (such as BCCH) of a cell only occupy one time slot of one carrier frequency in the cell (and cannot change channels or occupy several channels at the same time)?
4. Can the service channel and the control channel be in the same channel?

Test standard for domestic GSM mobile phone network access detection

At present, China's GSM mobile phone network access testing is carried out in 1996, YD / T 884-1996 "Technical indicators and test methods of 900MHz TDMA mobile station equipment in digital cellular mobile communication network". The standard is based on chapters 12-14 of ETSIMG 11.10, which mainly defines the definition, requirements and test methods of the radio frequency and audio specifications of GSM900 wireless transceivers. In addition to the mobile phone network access test, the standard is also widely used in arbitration testing, performance testing, and testing of mobile phones by mobile phone manufacturers, operating units, and maintenance departments. The main indicators specified in the standard are:

transmitter:

-Phase error and frequency error

-Frequency error under multipath and interference conditions

-Transmitter carrier frequency peak power and burst timing

-Output RF spectrum

Receiver:

-Bad frame indication performance

-Reference sensitivity

-Receiver input level range

-Co-channel suppression

-Adjacent channel suppression

-Intermodulation suppression

-Suppression of blocking and spurious response

Stray radiation

Audio test:

-Sending sensitivity / frequency response

-Send loudness evaluation value

-Receive sensitivity / frequency response

-Received loudness evaluation value

-Side-tone masking evaluation value

-Phone acoustic coupling loss

-distortion

-Out-of-band signal suppression

-Idle channel noise

Since its promulgation, YD / T 884-1996 has unanimously guided the testing of China's GSM mobile phones, and has played a technical support and guarantee role in ensuring the quality of domestic network access and sales of GSM phones. However, with the continuous development of GSM technology, GSM dual-band and multi-band mobile phones are now on the market, and new functions and new functions of mobile phones are constantly emerging. The standard only covers one 900MHz frequency band, so it is urgent to update. At present, China Wireless Communications Standards Committee (CWTS) is studying and formulating new standards.

Test standards and technical requirements for domestic GSM mobile phone network access detection

At present, the domestic network access testing of GSM mobile phones is carried out by sampling.

When a mobile phone manufacturer applies for a new type of mobile phone to access the network, it must complete all procedures in accordance with the "Administrative Measures for the Approval of Telecommunications Equipment Network Access" of the Ministry of Information Industry. The Ministry of Information Industry entrusts the local industry authorities to randomly sample 5 mobile phones that apply for network access, together with the test The attachments, including special RF test cables, batteries, chargers and instructions, are sealed together and sent to a testing center authorized by the Ministry of Information Industry for inspection.

Basic functional tests include:

-Location registration

-Mobile calling conversation

-Mobile called

-Mobile station hang up

-Switch

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