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A multicarrier MFSK channel coding scheme

In Electronic Infomation Category: A | on April 14,2011

Abstract: With the upgrading of hardware and SP8715 datasheet and coding techniques, mature multi-carrier technology in the communication process has been widely promoted and SP8715 price and applied. In order to more severe multipath fading conditions for higher spectrum efficiency, the use of static multi-tap channel modeling approach to simulate the propagation of radio signals. The channel impulse response analysis of the data error rate as the basis for design of a the introduction of orthogonal frequency division multiplexing technology and SP8715 suppliers and the concept of multi-antenna multicarrier MFSK improved coding scheme, and validated in a multi-path fading conditions of the spectrum efficiency and error rate, which proves the efficiency of the program in terms of improving the feasibility of the spectrum.

0 Introduction

Mobile wireless channel in real, complex channel impulse response is a function of time with delay-related. Has documented a variety of mobile radio channel impulse response model compound can be described as a form of usage statistics of the complex-valued zero mean Gaussian process. Which, when the complex envelope consistent with Rayleigh distribution, known as the Rayleigh decay channel, when the wireless complex envelope contains a fixed scattering source, do not meet the zero-mean process, Rice fading channel. Rayleigh and Rice with a typical multi-path fading model, the paper mainly experimental model considered the signal free of direct spread Rayleigh fading channel model.

Present, common or ordinary single-carrier frequency division multiplexing wireless systems, multipath fading for a balanced receiver is the main approach to the suppression, in terms of cost and efficiency is not very ideal. The multi-carrier orthogonal frequency division multiplexing (OFDM) and multi-antenna transceiver array (SIMO / MISO / MIMO) can be combined to meet the expansion of available spectrum to a large extent the same time, but also in smaller hardware expenses costs to complete suppression of multipath effects. Therefore, OFDM + MIMO wireless as a viable solution in theory, a great deal on the transmission efficiency and enhance control of the bit error rate associated validation experiments. However, in view of the code associated with the program too complicated, long time, the system has long been associated with only a stop on the theoretical studies.

In order to maximize the spectral efficiency and high-OFDM multi-antenna coding anti-interference ability and take into account the complexity, consider a single carrier OFDM information capacity of the highly compressed, difficult to abandon the cause of the multilevel coding complex modulation envelope of calm detection scheme, eventually to become only the expression of a dual band signal characteristics of the switches (ON-off keying) the carrier, formation of the MFSK transmitter multi-carrier signal data block. Meanwhile, MIMO transceiver also further simplify the system, only retained in the system of multi-antenna single-ended form, creating a single overcharge (SIMO) and multiple single-income (MISO) antenna system no longer has the advantage on the transmission rate However, multipath effects are still retained a high respect diversity gain.

1 basic encoding process

Shown in Figure 1, the system according to the data block mode OFDM multicarrier MFSK coding structure, which contains the longitudinal axis of the total available frequency spectrum band, the horizontal axis for the communication time, so that a multi-carrier data blocks within MFSK the formation of a number of full-frequency slots, each slot according to a certain frequency can be divided into several wide frequency bands, each frequency band and can be characterized by a binary switch sub-carriers.

A number of subcarriers N = 8 multicarrier MFSK system also needs to be divided within each time slot sub-band 8.

Figure 1 Multicarrier MFSK data block structure

Subcarrier modulation code into the slot of the process in accordance with the following rules, namely, shown in Figure 2. All sub-carrier channel frequencies in accordance with M = log2 (N) are numbered. For example, when N = 8, the sub-carrier channel can be divided into a total of eight sub-bands 0-7.

Input from the source sub-band sequence number can only be marked in accordance with the rise into a slot, once the latter number is not greater than the previous number, the latter number must be calibrated into the next slot. For example, in Figure 2 the sub-band sequence number set up arrangement is 1-2-3, then the number three carrier can be calibrated at the same time slot. But when the source of sub-band group number 2-2-3, the first time slot only a single calibration of the number 2 slot in the second to be able to calibrate the rest of the band group 2-3 in ascending order. Development of coding rules that the benefits and features of the following: First, the use of orthogonal frequency division multiplexing to carry out the concept of sub-band modulation, the modulation technology maturation process is simple, a time slot within the same frequency band simultaneously sequence multiple calibration number, the total transmission capacity of the channel is larger and their ability to have some anti ISI; the second is used in the calibration sub-band within the time slot instead of the traditional single-carrier modulation used in communications vulnerable to the decline of the multi-level multi-band modulation way, in case the amount of data is not affected greatly enhanced anti-jamming capability; third multicarrier MFSK in the use of block similar to the fixed-bandwidth asynchronous transfer mode + FIFO transfer mode to solve the possible use of synchronous transmission increase the complexity of the system caused the problem.

multicarrier MFSK Figure 2 calibration block slot rules

2 multi-tap multipath channel transmission model

When using the statistical approach to channel modeling, usually there are three ideas to consider:

Set fading delay and amplitude, and then multiplied with the channel and the sum, this is the most simplified multipath channel simulation;

Set the path delay of the delay and power, according to re-route power tap coefficients are obtained real and imaginary parts, and then multiplying the complex tap coefficients and the summation signal;

multi-path effects will be seen as FIR filter simulation.

Paper the multi-tap models and methods more similar.

And real to simulated urban environment is similar to the complex set of tap coefficients, a city with a group of 6 tracks measured gain data [-20 0 -7 -12 -18-22] dB. Which, when a path gain value less than the maximum diameter of 20 dB or more, that the path has no effect on the system, that after this set of data conversion can be simplified as [-6 1 -9] dB. In the calculation, the actual output string rb energy can be expressed using the following formula:

Rb = 16 Sb (h1 + h2 + h3) +2 Sa h3 +2 Sc h1 + (Sa + Sb) h2,

In a row through the discrete multipath string equivalent model can be obtained by this method of discrete approximation of the approximate character output and the corresponding output of energy.

3 coding scheme and the antenna transmission system improvements

Using basic coding, because under natural conditions simulated in the sub-carrier channel completely random sequence inherent in the lifting arrangement of the number of statistical law, efficiency and the use of a single time slot is not particularly high. To this end, improved during the encoding scheme, consider two simple ways to increase the efficiency calibration of a single time slot.

Improved method first, through the calibration of each slot were calculated before and ascending and descending order can calibrate the number of occupied sub-bands to elect a large number of the sort used as the current program This calibration is completed in each time slot occupied by only a certain specific frequency bands can be used to identify the current rise in descending order. This approach has the advantage of improving the input data does not require too much re-operation that is able to play a certain optimization.

Ways to improve Second, during the time slot before the calibration, set the four data cache. Given the length of a certain number of subcarriers data string as a unit, the serial number of subcarriers occupied by all the band into the restructuring of the four buffers. Into the buffer rules are as follows: First, from an ascending or descending selected as the standard, in accordance with the basic coding method carried out at the first slot buffer calibration, when you need a new form into a new time slot second cache, and so on. When all four registers and then jump back to the No. wheel mounted over the second slot buffer calibration cycle, until a certain length of the serial number given all of the data string into the buffer until the four. In the subsequent course of transmission to buffer the unit from One to Four were in turn sent the same set of four receiver FIFO buffer asynchronous transfer mode according to the data string recovery decoding. Advantage of this approach to re-register the unit calibration process, changed the original random statistical laws of nature, in this mode, there is little common basic coding scheme occupies a single slot of the subcarrier situation, the spectrum utilization efficiency greatly improved. The disadvantage is that the hardware storage and computing power demanding.

Transmission system in the improvement of the antenna, through spatial diversity means to strengthen the system against multipath interference. In signal transmission by the transmitter or receiver to send or receive signals with the two groups constitute more than single out or single-input, multiple out of MISO or SIMO system, in order to strengthen the diversity gain. Which is equipped with two antennas at the transmitter, the two antennas need to transfer the same data, so the system does not like the actual transmission data rate MIMO system that would increase exponentially. When using multiple antennas for receiving, in order to achieve the purpose of simplifying the system, usually carried out using equal gain combining ECG signal detection and consolidation. Improvement program of more than proven in the next section.

4 parameters of the design and experimental results

Improved coding scheme in the validation, the main spectral efficiency and bit error rates using the two indicators to assess the design plan. In this paper, spectral efficiency is defined by the following formula:

Where is the spectral efficiency, bn to send the total number of time slots, n for the current time slot number within the calibration of the number of subbands, L symbols for each sub-band occupation number of bits, and N is The total number of sub-bands.

Under this method, the basic coding scheme, for example, provided in the band is 16, the total number of sub-band number 10 000 cases for the experiment, the efficiency of the basic coding scheme is shown in Figure 3 results .

Figure 3, statistical coding efficiency

Figure 4 FSK and MFSK the efficiency of the basic coding scheme compared

Be seen from Figure 4, the total number of 16 bands set, the resulting time slot in order to calibrate a serial number or 2 sub-band based, specific statistical data such as Table 1.

probability distribution of tables Table 1 serial number

Although the overall efficiency of spectrum utilization

less than 0.5, but with no basic pre-encoded common than single-carrier FSK coding efficiency has been greatly improved upon, because under the same conditions, single-carrier FSK can only be reached:

Only the spectral efficiency of 0.25, which shows the basic coding scheme before the design is effective.

In another calculation, Figure 4 shows the total frequency division subcarriers from 2-1024 with the conditions, the single carrier and multicarrier MFSK FSK coding efficiency of the basic comparison shows the pass band, basic coding scheme always has a large efficiency advantage.

In order to further improve the basic coding scheme, better choice theory to verify the improvement program 2, the basic coding scheme and coding scheme to improve the spectral efficiency of 2 comparative results shown in Figure 5.

Figure 5, the program of basic and improved spectrum efficiency comparison

Visible, using the improved scheme 2, although the hardware complexity will cause some adverse effects, but the spectral efficiency relative to the common coding scheme, in 2-1024 by sub-carrier conditions, the total spectrum efficiency can be maintained in general about twice the encoding scheme. Shows the design of improved coding scheme 2 is successful.

Bit error rate, when the three-path gain is set to [-6 1 -9] dB, the normalized coefficient of the decline of [0.1817 0.7268 0.091], so available in Figure 6. According to Figure 6, the extent of the decline of sub-carriers, subcarrier can advance in the detection of hard decision to set a different threshold, the decision of each subcarrier can approximate error rate.

Figure 6, number of subcarriers N = 8 when the multipath fading power spectrum

Figure 7 shows the threshold set under the basic encoding scheme for each sub-carrier bit error rate (Es/N0 = 7dB, number of carriers N = 8), because the carrier 4 and 6,3 and 7, the decline in the value of band is symmetrical, so the only list in Figure 7, the carrier 3 and carrier 4.

Be seen, the channel bit error rate of the decline of energy have a greater impact, the basic coding scheme in the given conditions, although more efficient path, but the error rate under the shadow verdict is generally more than most 10-2 order of magnitude. The introduction of the concept of multi-antenna SIMO, use 1 to 4 groups receiving antenna equal gain combining ECG, the results shown in Figure 8.

Figure 7, the threshold set under the basic plan of each sub-carrier BER

Figure 8 ECG combined basic coding error rate

Can be seen from Figure 8, the basic coding scheme is designed with multiple receiving antennas in the combined ECG testing can effectively restrain the strong multipath effects caused by the larger error rate, resulting in a higher spectrum utilization efficiency, lower hardware costs in the * terms of the premise, but also access to a strong multipath suppression.

5 Conclusion

Paper designs a new type multi-carrier modulation coding scheme for MFSK class OFDM systems, and simulation shows the system in more serious under Rayleigh multipath fading spectrum efficiency and bit error rate characteristics. And the joint use of MFSK and SIMO OFDM modulation and transmit and receive other way, the proposed system is not in the system increases the complexity of the case is still in the strong interference conditions to obtain than individual single-carrier modulation with higher spectral efficiency and revenue than the single antenna one has better BER simulation results. Multicarrier MFSK encoding scheme is applicable to all types of work in a Rayleigh multipath fading conditions in the low-cost low-capacity wireless system improvement program.

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