TD-LTE system interference analysis

[Abstract] article on TD-LTE system inside and outside interference mechanism system analysis, and combined with the minimum requirements of the standard equipment performance is calculated for a typical case of system isolation requirements, as well as isolation realization.

[Keywords] TD-LTE interference isolation 1 Overview With the freeze TD-LTE standard equipment mature as well as the rapid development of mobile Internet business, TD-LTE has become the focus of the industry. TD-LTE system inside and outside interference network deployment must be considered one of the key issues.

Facing the TD-LTE system interference noise Pn interference Iinter Iintra-system and system-system interference within the system, the following analysis of these three interference.

2 noise, noise can be divided according to the source receiver internal noise and external noise. Receiver internal noise include the conductor thermal noise and amplifier noise amplification, the external noise is from the non-mobile communication transmitter in the receiver other than the electromagnetic wave signal, can be divided into natural noise and artificial noise.

Generally the main consideration in the analysis of the receiver internal noise, can be calculated by the following formula:

Pn = KTB + NF (1

K: Boltzmann constant (Boltzmann CONSTANT, 1.380662 × 10-23JK-1,

T: Kelvin absolute temperature taken at room temperature in the general calculation 290K

B: effective receiver bandwidth,

NF: the noise figure of the receiver, and generally the standard base station noise figure were 7dB.
As the occupied bandwidth changes due to the bandwidth of the LTE system in the 1.4MHz ~ 20MHz variable, and using OFDMA / SC-FDMA multiple access methods, the user actually occupies only part of the system bandwidth. Therefore, the thermal noise level of the channel also changes.

3 system interference in the interfering system is the interference between each of the radio network element transceiver unit in the present mobile communication system.

3.1 TD-LTE system of different users in the same cell under the same frequency interference downlink OFDMA uplink with the SC-FDMA multiple access methods, different users occupy different, mutually orthogonal sub-carriers, so there is no 3G system in the same cell The multiple access interference of the different users of the LTE system in the same frequency interference is the interference with other cells of the same frequency, which is also the LTE system interference coordination inhibit the technical problem to be solved.

Intersymbol interference in the uplink and downlink of the the 3.2 LTE TDD system of the LTE TDD system uses time division duplex mode, the downlink channel in the same frequency point by the transition point of the vertical line set the downlink channel may time slot occupied by the uplink and downlink between Since the time conversion point is inconsistent, and appear to "overlap" (simultaneous presence of the point in time of the uplink and downlink between the base stations are not synchronized or wireless signal propagation delay, etc., may cause the the eNode B cell or interference between the end-user.

ENode B (an adjacent cell sometimes inconsistent with the transition point of the vertical line in the cell between different frequencies if a second transition point of the adjacent cell to set different, is configured in the vertical rows in different time slots, there will be a cell eNodeB emission when another cell being received, and thus will appear more serious between the uplink and downlink interference as shown in Figure 1:

In order to avoid such interference, planning should pay attention to:

A combination of the regional uplink and downlink traffic demand characteristics, as far as possible in the same time slot allocation scheme in the area into pieces,
2 in a different region of the time slot allocation scheme at the junction of two adjacent different time slot allocation scheme of the cell, should have an occlusion occurs the overlapping time slot, or two adjacent cell by detecting overlapping timeslot interference strength, to decide whether to continue to allocate in the overlapping time slots.

(A loss of synchronization when the synchronization reference inconsistency between the adjacent cell, even if the inter-cell using the same transfer point, because of the different starting time, there will be time points "overlap" between the two adjacent cell in Figure 2 follows:
Usually using an external reference clock source (such as GPS or Galileo satellite system synchronization between the LTE eNode B when the external reference clock source has failed, and a synchronization process error is too large, there may be a loss of synchronization between the Node B according to the 3GPP TS36.133 requirements, using the same frequency and have overlapping coverage areas between the neighboring Node B, the time error of the beginning of the frames should be less than or equal to 3μs (coverage distance of less than 3km meet this requirement, the adjacent inter-cell the vertical line interference time is very short, little impact on network performance.

Synchronization between the base station of the LTE TDD system in planning, should satisfy this requirement.
(3 wireless propagation delay is greater than the conversion point guard slot with increasing propagation distance wireless signal propagation process, a propagation delay. Addition, mobile communications repeater extends cell coverage distance, also introduced The delay of the repeater equipment. propagation distance delay:

Δτ = d / c (2

Where, d is the propagation distance, c is the speed of light.
Within a cell, if the propagation delay is too large, will cause the terminal uplink interference to the other terminal in the vicinity of the downlink receiving formed in eNode B receiving end of each terminal upward signal synchronization, the terminal must advance The the UpPTS and sub-frame of time to transmit uplink as shown in Figure 3, the eNode B transmitting end time as a reference, the time advance to eNode B should be equal to the terminal a radio transmission delay τ, and also equal to the Node B of the downlink signal emitted reach the wireless transmission delay of the terminal if the terminal receives the downlink signal time as a reference, the timing advance is twice the wireless transmission delay (2τ.

With respect to the received downlink signal reference, since the terminal needs to transmit the uplink the UpPTS and sub-frame 2, if 2τ is greater than the guard interval GP between the DwPTS and UpPTS, will cause the terminal's uplink UpPTS channel interference to nearby 2τ The time advance amount The other terminal receives from the Node B DwPTS channel. therefore, in accordance with the following formula to determine the uplink and downlink interference does not produce the maximum transmission distance (ie, the maximum distance covered:
TGAP is the guard interval.
Was calculated according to the special sub-frame in the standard configuration, the maximum coverage distance of the different special subframe configuration format of the TD-LTE base station, as shown in Table 1:
If there is a forwarding device such as mobile communications repeater, signal propagation delay due to the filter pieces inherent delay within the repeater equipment and fiber optic media, will lead to further reduced the above delay guard interval corresponding to the maximum distance covered.

Taking into account the interference signal after distant propagation loss, the signal power is relatively weak, the project is generally considered less the influence of interference.

(4 adjacent channel interference due to the device filtering characteristics of the non-ideality, interference use adjacent frequencies between the parties.

Assuming the same as the distribution of the terminal number and location on different frequencies, ACS and ACLR index requirements of the receiver point of view from the 3GPP standard (usually in more than 30dB with respect to the same frequency interference, adjacent channel interference to the receiver smaller than 30dB adjacent channel interference frequency interference than the same weak more than 1,000 times and can be ignored.

4 inter-system interference interference between 4.1 system type can be divided into the adjacent channel interference, stray radiation, receiver intermodulation interference and obstruction from the perspective of the formation mechanism of interference.

(1 adjacent channel interference (ACI

Adjacent frequencies assigned to the different systems, the adjacent channel interference occurs. Transceiver device filtering performance imperfect work in launch opportunities adjacent channel leakage signal to the receiver operating band interference while interfere with the receiver also receives the working band other than the transmitter signal. decided the key characteristics of the interference indicators transmitter the ACLR and receiver of the ACS.

(2 stray radiation (Spurious emissions

Generating a radiation signal component (excluding the band radiation outside a predetermined frequency band, including the thermal noise generated by the electronic thermal movement due to the non-ideal transmitter part of the operating characteristics of the amplifier, mixer, filter, etc., within a very wide range of the working bandwidth , various harmonics, spurious radiation, frequency conversion, product and a transmitter intermodulation.

Adjacent channel interference and stray radiation is considered interference in the adjacent channel interference transmitter leakage signal is interfered receiver in which the band distance band jammers work closer, the band have not yet reached the provisions of the stray radiation outside the band that effective work of more than 2.5 times the bandwidth (or the operating bandwidth of the upper and lower boundaries 10MHz Working frequency difference of more than 2.5 times the bandwidth of the two systems (or separated by more than 10MHz filter non-ideality is mainly manifested as spurious interference.

(3 receiver intermodulation interference receiver intermodulation interference, including the formation of multiple sources of interference intermodulation intermodulation emission component interference source (TxIMD, cross-modulation (XMD interference.

Multiple sources of interference formed intermodulation is due to the interference system receiver RF devices nonlinear, intermodulation products generated when two or more interfering signal component of relatively high intensity.

Emission component and the interference source is formed of intermodulation is due to the filter characteristics of the duplexer is not ideal, caused by the emission component of the interfered system leak to the reception side, thus with the source of interference is formed on the nonlinear device intermodulation.

The cross-modulation is also due to the receiver caused by the nonlinearity in the nonlinear receiving device, interference amplitude modulated transmission signal of the system is mixed with close to the receive band of the narrow-band interference signals, will produce a cross-modulation.

(4 blocking interference blocking interference not fall interference system within the reception bandwidth. However, due to the interference signal power is too strong, and the receiver's low noise amplifier (LNA push saturated zone, it does not work by interfering system allows blocking interference power requirements generally lower than LNA 1dB compression point of 10dB.

Forming characteristics under different interference, adjacent channel interference and spurious interference, intermodulation interference are fall within the interfered system receiver, which receives the deterioration of communication quality, blocking interference in the interference system outside the reception bandwidth, hinder communication system receiver would be disturbed push saturated.

To fall within the reception bandwidth of the interfering system interference can be performed on the power sum of the total interference power:

, PACI, PSE, PIMD were adjacent channel interference, stray interference intermodulation interference in dBm.
Under normal circumstances, the three intensity of the interference difference between the larger, the synthesis of interference power will depend primarily on one of the largest one, even in the most extreme case, the three kinds of interference equal intensity, the total interference power increase 4.5dB, still meet the the interference indicators left margin requirements in the general project generally accounted for separately each interference to meet the requirements of system indicators, in order to simplify the analysis.

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4.2 inter-system interference analysis method interference analysis many ways, 3GPP TR36.942 mentioned there are two types: deterministic calculation and simulation methods.

(A deterministic calculation method is also referred to the minimum allowed coupling loss MCL (Minimum Coupling Loss calculation method the deterministic calculation advantage of the method is simple, can be more easily obtained theoretical estimation result, the calculated results corresponding to the most adverse conditions corresponding MCL requirements more stringent.

Deterministic calculation method is based on the relevant parameters of the interfering system, and the interfered system, and to calculate the system to achieve the necessary interference suppressing the minimum required to allow the coupling loss the MCL. Generally MCL calculated using the following formula:

MCL = output power of the source of interference - attenuation - the allowable interference level (5

Transceiver ACS / ACLR or spurious signal power requirements were intermodulation suppression, combined with its bandwidth and transmit power can be calculated to achieve a certain interference suppression requirements of MCL.

An attenuation of the different types of interference are taken as different parameters:

Adjacent channel interference is ACIR,

Intermodulation interference intermodulation rejection ratio.
2 allows the interference level on the in-band interference can generally be determined according to the allowable degree of deterioration of the reception sensitivity of (subsequent calculations fetch deterioration amount is 1dB
The blocking interference of the band is determined generally by receiving equipment LNA 1dB compression point.
Other gain and attenuation due to the indicators of the transceiver antenna connection at defined coupling loss CL including antenna relative gain antenna space loss, signal attenuation of the applied filter feeders and attenuation of the joint part, increased external filtering device, further comprising the signal attenuation of the filtering device.

(2 simulation method simulation method to set the interference system and interfere with the base station of the system, the transmission power of the terminal, the load of the base station, through simulation derived inter-system interference in the setting environment simulation method consider the impact of power control, user distribution of inter-system interference, it is a more comprehensive inter-system interference analysis, particularly in relation to the terminal interference scenarios.

4.3 System isolation requirements on deterministic calculation method according to the standards of the receiver and transmitter performance requirements, the use of LTE and other systems (including the isolation requirements of the different operators of the LTE system, as shown in Table 2:

Corresponding to the result of the above calculation, in the actual system applications need to pay attention to the following two points:

(1 or more deterministic calculation result is considered in accordance with the single carrier transmitter, if the interference system the actual configuration of the N carrier, assume that the maximum transmission power of each carrier are the same, the interference power will increase exponentially and therefore isolation requirement corresponding increase lgN (dB.

(2 above interference isolation results are in accordance with the minimum requirements of the standard, the actual performance of the system equipment (such as CDMA base station spurious suppression level should be better than the standard requirements of actual network, base station isolation requirements should be combined with the performance of the specific equipment to be accounted for.

Interference between 4.4 system solutions in general, the interference between systems solutions are mainly two: antenna spatial segregation and installation of isolation filter. Spectrum resources are relatively well-off can be flexibly configured carrier guard band.

(1 antenna space isolation antenna space isolation is of the interfering system transmitter antenna with the interfered system is receiving antenna to maintain a certain degree of physical space distance (angle, so that the transmitting antenna waves through space is attenuated meet to reach the receiving antenna end of the deterioration of electrical flat extent.

According to the construction of the physical environment, can take advantage of the the Tower or days face different platforms, different position antenna spatial isolation, specific horizontal isolation, the vertical isolated and mixed isolation three ways.

The level of isolation and distance relationships are as follows:


Vertical isolation and distance relationships are as follows:


Ih: jamming systems transmitting antenna system receiving antenna interference level of isolation (dB,

IV: interfering system transmitting antenna with the interfered system is the vertical separation of the receiving antenna (dB,

GTx: jamming systems transmitting antenna toward is interfering with the launch of the system receiving antenna gain (dBi

GRx: jamming system interfere with the system receiving antenna toward transmitting antenna receive gain (dBi

dh: the antenna horizontal spacing,

dv: the antenna vertical interval,

λ: radio wavelengths, such as stray interference should be taken as interference system receiver band wavelength, such as blocking interference, should be taken as interference emission band wavelength. dimensionless keep dh, dv same.

Assuming GTx + GRx = 0dBi, according to the above formula to calculate the spatial isolation between the system requirements, as shown in Table 3:

Based on the calculation results of the Table 3, EV-DO, and LTE vertical distance required 7m above, it was very difficult to implement. Fact, according to the measured study of the antenna isolation, the day, the line spacing is relatively far, isolation is less than experience formula results, even if the vertical distance of 7m, it is difficult to achieve 100dB isolation 50dB ~ 70dB isolation. ordinary antenna co-location can only be seen EV-DO base station antenna is difficult and TD-LTE base station antenna co-located construction, to be combined with days face natural or artificial barrier to increase the isolation between the antenna GSM system and TD-LTE system total station, and also to ensure sufficient vertical isolation, in order to avoid mutual interference.

(2 retrofit isolation filter filter is divided into two types: band stop filter and a band-pass filter. Specific network design should pay attention to:
1 on the same frequency additive interference need to originator retrofitting band stop filter to reduce the power in the receive band, in the closed end of the installation you need to block interference band-pass filter to reduce the power in the receive band.

2 as far as possible using the the antenna erected position of the obstacle, the method may additionally be used to increase the isolation plate.
3 transmit filter performance for each frequency narrowband filter to filter, can reduce the antenna isolation requirements.
4 linear amplifier, reducing the the amplifier signal after stray.
According to the results of analysis of adjacent channel interference between LTE FDD and TDD systems adjacent channel can not coexist future do frequency planning, if conditions allow, should leave sufficient guard band to avoid different carriers LTE FDD and TDD system adjacent channel coexistence. adjacent if LTE system downlink transmit band and existing 2G/3G system uplink reception band, or LTE system uplink receiver frequency bands and existing 2G/3G systems downstream emission band adjacent advised to stay sufficient guard band to avoid adjacent channel interference affect system performance.

5 summarizes the uncertainty analysis, in addition to the EV-DO system, generally through spatial isolation to meet interfere with isolation of TD-LTE system and other system requirements. Addition, note that the results of this paper is based on the standard minimum requirements actual device performance is generally far better than the minimum requirements of the standard and the actual carrying out of the network design, in accordance with the specific equipment performance recalculated interference isolation requirements.


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