The key anti-jamming technology of the third generation mobile communication system

1 Introduction

The mainstream standard wcdma/td-scdma/cdma2000 of the third generation mobile communication system adopt the Code Division Multiple access method, CDMA Code division multiplex System is a disturbance restricted system, in the transmission of information, there are multiple access interference, multipath interference and far-near effect. Any technology that can improve the anti-jamming performance of the system can improve the capacity of CDMA system, in this paper, the key anti-interference technology of the third generation mobile communication system is introduced, aiming at the various interferences in the mobile communication. These technologies include: Air Division Multiple Access Smart antenna technology, used to resist multipath interference rake reception technology, anti-multiple access interference detection technology, and the performance of these technologies in a specific system simulation.

2 Smart Antenna

The smart antenna uses the combination of multiple antenna elements for signal processing, and automatically adjusts the transmit and receive pattern to achieve optimal performance for different signal environments. Smart Antenna is an Air Division multiple access (SDMA) technology, which mainly includes two aspects: spatial filtering and DOA estimation. The main idea of spatial filter (also called beamforming) is to use linear filtering technique to restrain interference and noise as much as possible to obtain the best signal estimation by using the spatial distribution of signal, interference and noise.

The smart antenna controls the weighting by the adaptive algorithm, adjusts the antenna's pattern automatically, causes it to form 0 traps in the jamming direction, cancels the jamming signal, and forms the main beam in the direction of the useful signal to restrain the interference. The automatic adjustment of weighting coefficients is the forming process of beam. The smart antenna beamforming greatly reduces the multi-user interference and reduces the small interval interference. (Computer science)

3 2d-rake Receiver

Principle of 3.1 2d-rake receiver

The ability of intelligent antenna to restrain jamming is limited by the number of antenna array in most cases, and when there are many unrelated multipath in the signal of interest, the array only retains one signal, and the Zero Trap is aligned with the other signal, so that the array can reduce the interference caused by the unrelated multipath, but fail to play the advantage of the path diversity. Thus is the second best. Therefore, the joint time domain and the space processing receive technology becomes the research hot spot.

When multipath delay propagation is present in the channel, and the time delay is greater than that of a single chip cycle, these multipath signals are both multipath interference and some valuable diversity sources, resulting in 2d-rake receivers. At present, the most discussed 2d-rake receivers are used in WCDMA uplink.

The space-time rake receiver Firstly beam the multiple path components with angular extension to reduce the multiple access interference or the unrelated multipath component of the expected signal generated by the other signals of DOA, and then send the filtered signal into the rake consolidator. To make full use of the energy of multiple paths of delay-distinguishable desired signals. Spatial beamforming is designed to attenuate interference signals, whereas time multipath mergers are designed to use useful signals.

In contrast to the one-dimensional interference suppression in Time-domain and airspace, the space-time two-dimensional interference suppression no longer uses the forced zero condition, but considers the existence of the noise and uses the optimization criterion. There are two optimization criteria for space-time processing, one is the space-time minimum mean square error criterion, the other is the space-time maximum likelihood criterion (customarily called the maximum likelihood sequence estimation mlse criterion).

3.2 2d-rake Simulation Environment parameter settings and assumptions:

WCDMA Uplink, IMT-2000 vehicle a channel model, antenna array antenna using 8-array Uniform line array, the array interval is 1/2λ.

Physical layer parameters in line with WCDMA requirements: 1 Carrier frequency: 2GHZ 2) chip rate: 3.84MCPS 3) sampling rate: 3.84*8=30.72msps;4) OVSF Spread spectrum: DPDCH (256), DPCCH (5); No consideration of channel coding and interleaving; 6 User Kasami code scrambling

3.3 Simulation Results Analysis:

(1) When the line is not overloaded (the number of users is less than 8), the 2d-rake receiver has better performance than the traditional rake receiver, and can effectively counter the multiple access interference.

(2) The traditional rake receiver in the absence of channel coding 4 users, due to multiple access interference, BER in 10-1 of the floor effect, while the 2d-rake receiver can achieve 10-2 of the following performance, but in the 10-3 floor effect. To achieve better performance, you must rely on channel coding techniques.

4 Combined detection Technology

The traditional reception technology is for a user to signal detection and other users as noise processing, in the increase in the number of users, resulting in a deterioration of signal-to-noise ratio, system performance and capacity are unsatisfactory. The joint detection technology is based on the traditional detection technology, make full use of all user signals that cause multiple access disturbances and their multipath prior information (the correlation between signals is known: for example, an accurate user channel code, each user's channel estimation), the separation of the user signal as a unified and interrelated joint detection process to complete, Thus it has excellent anti-interference performance and reduces the requirement of the system to the power control precision, so it can make use of uplink spectrum resource more effectively, improve system capacity significantly, and weaken the effect of "far-near effect".

Application of 5 smart antenna Combined Detection (SA+JD) in TD-SCDMA

The working principle of 5.1 SA+JD

The TD-SCDMA system combines smart antennas and joint detection techniques: 1 The smart antenna eliminates the interference between the cells, the joint detection eliminates the interference in the cell, the two use together; 2 the smart antenna alleviates the influence of the inaccurate channel estimation on the deterioration of system performance in the joint detection process; 3 when the user increases, The computation of joint detection is very large, and the use of smart antenna reduces the potential multi-user. 4 the array number of smart antenna is limited, for M-array smart antenna can only suppress M-1 interference source, and the formation of Sidelobe for other users is still interference, can only be combined with joint detection to reduce these disturbances; 5 in the High speed Mobile, TDD mode on the downlink using the same space parameters to make the beam forming a deviation When the user is in the same direction, the smart antenna can not play a role, and the multipath interference caused by more than one bit of time delay need joint detection to make up.

5.2 SA+JD Emulation Environment parameter setting:

TD-SCDMA uplink, single cell, IMT-2000 indoor, pedestrian and vehicle A-channel model, antenna array antenna using 8-array uniform line array, array interval of 1/2λ.

Physical layer parameters comply with TD-SCDMA requirements: 1 Carrier Bandwidth 1.6MHz 2) chip rate: 1.28MCPS;3) does not consider channel coding and interleaving.

5.3 Analysis of simulation results

The simulation results show that the TD-SCDMA system can work in full yards in three kinds of multipath environments required by ITU, and has good anti-jamming performance by combining intelligent antenna and joint detection.

The prospect of anti-jamming technology of the third generation mobile communication system 6

The joint detection is used to solve the problem of interference among multiuser, while Rake is accepted to solve multipath interference problem, although the two can not be directly compared, but the algorithm of rake receiving before joint detection is realized. In addition, the third generation system is more rigorous to the Doppler frequency shift, how to increase the number of rake receiver branch, the effective separation, adjustment, selection and merging of multipath, need to be more in-depth study.

Due to the complexity and cost of the system, smart antennas and joint detection are mainly used in base stations, and the next step is to explore the feasibility of using 2d-rake or interference cancellation (IC) in mobile terminals. In addition, this paper proposes a downlink multi-user transmission technology--joint-Send (JT), which is to transfer joint detection to the sender to execute, in order to improve the actual data transmission rate of downlink and simplify the design of mobile station.