CN1691562B - CDMA access method based on orthogonal time-frequency domain with variable spread spectrum and frequency hopping - Google Patents

Abstract

A code division multiple access switch-in method based on the orthogonal time frequency domain of the changeable spread-spectrum and hopping frequency comprises the steps of: a) according to the pattern of the hopping frequency, selecting proper time frequency unit groups in the OFDM time frequency domain; b) selecting orthogonal code from the orthogonal code groups, in the OFDM time frequency unit group that selected in step a), using orthogonal spread-spectrum to confirm the sub message channel of the selected hopping frequency; c)multiplying the selected groups of time frequency unit from step a), from the same time frequency unit groups in step b) that meet the orthogonal characteristic; d) transmitting the multiplied data from the step c) through the OFDM system.

Description

CDMA access method based on the quadrature time-frequency domain of variable spread spectrum and frequency hopping

Technical field

The present invention relates to message transmission and multiple access technique in the wireless communication system, particularly in OFDM (OFDM) system, utilize orthogonal spectrum expansion and frequency hopping to carry out the method for message transmission and multichannel division.

Background technology

At wireless communication field, multiple access technology is used to support a plurality of user access networks, thereby reaches the multiplexing effect of multi-user service.Along with the expansion of business demand in the radio communication, provide the transfer of data of higher rate and multiple access technique just to become a research focus.Code division multiplexing (CDMA) is the radio spread spectrum communication technology that is used for a kind of advanced person of digital mobile cellular telecommunication in recent years, and by IS-95, Wide band Code Division Multiple Access standards such as (W-CDMA) and system adopt.Code division multiplexing (CDMA) system adopts direct sequence spread spectrum (DS-SS), to overcome the frequency selective fading in the channel.But its capacity is subject to multiple access and disturbs (MAI, multiple accessinterference), and MAI derives from the auto-correlation and the their cross correlation of incomplete spreading code.Zero cross-correlation orthogonal code is not introduced MAI in falt fading channel and Gaussian channel, but in frequency selective fading channels, disturbs owing to cut between general (chip), and the orthogonality of orthogonal code is difficult for guaranteeing that this will cause the reduction of systematic function.A kind of method that suppresses to cut general interference in frequency selective fading channels is with CDMA technology and multi-carrier modulation, and is combined as OFDM (OFDM) technology, to reach higher spectrum efficiency.CDMA multiple carrier (Multi Carrier-CDMA, MC-CDMA) and the orthogonal frequency domain code division multiplexing (Orthogonal Frequency and CodeDivision Multiplexing OFCDM) is exactly typical case's representative of the access way that combines of CDMA and OFDM technology.

In MC-CDMA mechanism, at frequency domain, the spreading code of user's appointment and the copy of the same information code element spread spectrum information that obtains that multiplies each other is mapped to different subcarriers, because the copy of same information code element transmits by a plurality of subcarriers, so realized the frequency diversity effect, but being still within the bounds of possibility of MAI.

Based on MC-CDMA thought, people such as S.Abeta are at " Performance of coherentmulti-carrier/DS-CDMA for broadband packet wireless access ", IEICE Trans, Commun., E84-B, n0.3, pp406-414, Mar., orthogonal frequency domain code division multiplexing (Orthogonal Frequency and Code Division Multiplexing, OFCDM) technology have been proposed in 2001 lists of references.The same with MC-CDMA, OFCDM carries out spread processing at frequency domain, thereby OFCDM has identical transmitting-receiving model with MC-CDMA.But OFCDM can change spreading factor according to factors such as cell structure and channels, thereby adapts to multiple communication environment requirement.Subsequently, people such as Noriyuki Maeda are at " Variable spreading factor-OFCDM with two dimensional spreadingthat prioritizes time domain spreading for forward link broadband wirelessaccess " Vehicular Technology Conference, 2003.VTC 2003-Spring, Volume 1, April 22-25, in 2003 lists of references, time-frequency domain is arrived in orthogonal spectrum expansion technology popularization among the OFCDM, and be the orthogonality of orthogonal code behind the assurance experience frequency-selective channel, mainly studied the time-frequency compound mode in coherence bandwidth and coherence time.

The experience frequency selective fading channels can cause cutting general interference, thereby the orthogonality of orthogonal code just is difficult for guaranteeing that this will cause the reduction of systematic function.A kind of method that suppresses to cut general interference in frequency selective fading channels is with CDMA technology and multi-carrier modulation, as OFDM (OFDM) technical combinations, to reach higher spectrum efficiency.

In MC-CDMA mechanism, at frequency domain, utilize the spreading code of user's appointment and an information code element to multiply each other and obtain spread spectrum information, spread spectrum information is mapped to different subcarriers subsequently.Because the copy of same information code element transmits by a plurality of subcarriers, therefore realized frequency diversity.

OFCDM can change spreading factor according to cell structure and channel condition, thereby adapts to multiple communication environment requirement.And be the orthogonality of orthogonal code behind the assurance experience frequency-selective channel, mainly studied the time-frequency combination in coherence bandwidth and coherence time.

No matter but MC-CDMA and OFCDM system, receiver all need have benefited from channel estimating and channel equalization to the decoding of spread spectrum information.For the OFCDM system, all will destroy orthogonality especially, introduce MAI the inconsistent of channel estimation bias in the extension field of an orthogonal code.Even to carrying out channel estimating, also be difficult to keep the deviation of the channel estimating of a unanimity at coherence bandwidth and the spread spectrum information in coherence time.

Summary of the invention

The CDMA access method that the purpose of this invention is to provide a kind of quadrature time-frequency domain based on variable spread spectrum and frequency hopping.

For achieving the above object, a kind of CDMA access method of the quadrature time-frequency domain based on variable spread spectrum and frequency hopping comprises step:

A), select suitable time frequency unit group at the time-frequency domain of OFDM according to frequency hopping pattern;

B) from orthogonal code sets, select orthogonal code, in the OFDM time frequency unit group selected, adopt orthogonal spectrum expansion to determine the subchannel under the selected frequency hopping pattern by step a);

C) in group selected from step a), carry out multiplexing to the spread spectrum information in the SC-SFHP channel of in identical time frequency unit group, from step b), selecting that satisfies orthogonal property with identical time frequency unit;

D) from step c), obtain multiplexing after data message carry out transfer of data by ofdm system.

The present invention adapts to the needs of following high data rate transfer.Because orthogonal spectrum expansion can provide the effect of system frequency diversity.Under the high spreading factor and under the frequency hopping effect, provide the effect of system time diversity simultaneously.Frequency hopping information required synchronously and to the despreading of orthogonal code can have benefited from ofdm system synchronously and channel estimating/channel equalization.Be convenient to the multiple communication environment of system's flexible adaptation, be 1 when becoming spreading factor, VSFH-OTFCDM is reduced to FH-OFDMA, is fit to single cell system.When becoming spreading factor greater than 1, VSFH-OTFCDM will be in conjunction with orthogonal spectrum expansion, and technology such as frequency hopping and OFDM are fit to multi-cell system.

Description of drawings

Fig. 1 is the structural map of the subchannel SC-SFHP under the selected frequency hopping pattern;

Fig. 2 is the composition framework of VSFH-OTFCDM;

Fig. 3 is that the time-frequency of the orthogonal spectrum expansion SC-SFHP channel of VSFH-OTFCDM distributes schematic diagram;

Fig. 4 is the signal model of VSFH-OTFCDM;

Fig. 5 is the allocation example of SC-SFHP channel orthogonal code.

Embodiment

The OFDM technology adopts the subcarrier (sub-carrier frequency) of mutually orthogonal to transmit the communication that low-rate data is realized high data rate concurrently.Receiving terminal utilizes the orthogonality of its each subcarrier, isolates the data message of parallel transmission.Based on the OFDM technology, the present invention proposes the code division multiple access access technology (VSFH-OTFCDM) based on the quadrature time-frequency domain of variable spread spectrum and frequency hopping.VSFH-OTFCDM combines orthogonal spectrum expansion, frequency hopping and OFDM technology, its thinking is exactly to utilize frequency hopping and become subchannel (the Sub-Channelunder a Selected Frequency Hopping Pattern of spreading factor under the selected frequency hopping pattern of the common control of time-frequency domain, SC-SFHP), with the data message orthogonal spectrum expansion, information mapping behind the spread spectrum arrives the SC-SFHP channel of time-frequency domain, and transmits by ofdm system.

Wherein, SC-SFHP is to the least resource of traffic assignments in the VSFH-OTFCDM system.The time frequency unit group that the SC-SFHP channel Mapping is formed to a plurality of time frequency unit TFC, each TFC can be made up of more than or equal to 1 frequency domain continuous sub-carriers one group of number, and the subcarrier combination mode among the TFC can be frequency domain continuous sub-carriers combination or make up by the index of subcarrier.The compound mode of TFC is by the frequency hopping pattern decision that distributes in the SC-SFHP channel.Allow a plurality of SC-SFHP channel stacks of satisfying orthogonal property in the sign indicating number territory of same time frequency unit group, can distribute to same user, also can distribute to different user at the SC-SFHP channel of sign indicating number territory stack.

According to the present invention, a plurality of OFDM code elements are formed the time-frequency domain of OFDM, and the VSFH-OTFCDM system controls the distribution of its time-frequency domain resources and quadrature code channel based on variable spread spectrum and frequency hopping.Frequency hopping pattern is selected according to system requirements and business need by system, select suitable time frequency unit (TFC) group at the time-frequency domain of OFDM, orthogonal code is selected by demand by system from orthogonal code sets, in selected OFDM time frequency unit group, determine to adopt orthogonal spectrum expansion to determine suitable SC-SFHP channel, the code channel that has identical time frequency unit group and satisfy orthogonal property can carry out multiplexing, and the data message after multiplexing carries out transfer of data by ofdm system.Wherein, the orthogonal property of orthogonal code refers to two optional from orthogonal code sets different sign indicating numbers, integration in given interval, and its result is 0.The mathematical description of orthogonal property is supposition W _j(t) and W _k(t) (j and k are integer, and 0 j, k N-1) all is selected from same sign indicating number collection { W _i(t); T ∈ (0, T), i=0,1 ..., N-1}

${\∫}_0^T{W}_j\left(t\right)W_k\left(t\right)\mathrm{dt}=\left\{\begin{array}{cc}0& j\≠k\\ M& j=k\end{array}\right.$ , M is a real number

Finish ofdm system synchronously and know under the situation of the frequency hopping pattern of distribution and orthogonal code, receiving terminal is determined the time frequency unit group of system assignment in the time-frequency domain of OFDM, and utilize the correlation properties of orthogonal code, spread symbols information in the SC-SFHP channel that distributes is carried out despreading, thereby extract legacy data information.

Fig. 1 is the structural map of the subchannel SC-SFHP under the selected frequency hopping pattern.Select under module 102 controls at frequency hopping pattern, system finishes the function of determining the time frequency unit pack module 104 be made up of a plurality of TFC in the OFDM time frequency unit.System's utilization selects orthogonal code module 106 to select suitable orthogonal code to finish orthogonal spectrum expansion from orthogonal code sets.Data symbols (comprise modulation or unmodulated) signal is then finished repeatedly copy to the data symbol signal by data symbols signal replication module 104, and the copy number is identical with the length of the orthogonal code of selection.Via the orthogonal code that data symbols after the duplicating behind the data symbols replication module 104 and orthogonal code module 106 are selected, in multiplier module 110, finish wise multiplication, to form the spread symbols signal.Subsequently, the spread symbols signal arrives selected time frequency unit group with the spread symbols signal map in constituting SC-SFHP channel module 112, thereby constitutes the SC-SFHP channel.In selected identical time frequency unit group, utilize SC-SFHP channel quadrature laminating module 114, will finish the quadrature stack from the spread symbols of a plurality of SC-SFHP channels.Signal after the quadrature stack will transmit via ofdm system.

Fig. 2 is the composition framework of VSFH-OTFCDM.In the VSFH-OTFCDM system model, system will construct the SC-SFHP channel in the OFDM time frequency unit, the SC-SFHP channel will carry the spread spectrum business datum, and the spread symbols of a plurality of SC-SFHP channels can be finished the quadrature stack, and the signal after the quadrature stack will transmit via ofdm system.In this mechanism, variable bandspread factor of being selected (VSF) and frequency hopping pattern control, data symbols is by the orthogonal channel of orthogonal spectrum expansion to time-frequency domain, and the VSF spreading factor of selected orthogonal intersection can be selected according to network topology and system requirements.VSFH-OTFCDM supports the multiplexing of multi-user service.Suppose that the data that user A and B are arranged will transmit.The business datum of user A is through modulation module 202, transferred to information code element decomposing module 204, the information code element decomposing module decomposes user profile in each SC-SFHP channel by business demand, in this legend, the information code element decomposing module decomposes SC-SFHP channel 0 module 206 and SC-SFHP channel K module 218 with the business datum of user A.In this K+1 SC-SFHP channel, each functional module is identical.Wherein, in SC-SFHP channel 0 module 206, user profile is imported into carries out orthogonal spectrum expansion in the orthogonal spectrum expansion module 208, information behind the spread spectrum is finished the mapping of channel by SC-SFHP channel Mapping module 210, orthogonal spectrum expansion module 208 and SC-SFHP channel Mapping module 210 all are subjected to the control of VSF module 214 and frequency hopping pattern module 216, and the information after the SC-SFHP channel Mapping is imported into the mapping of finishing behind the TFC mapping block 212 subcarrier of appointment.For descending (base station is to travelling carriage) transfer of data, system is that the SC-SFHP channel that a plurality of users distribute can carry out the code channel stack in base station transmitter.As shown in Figure 2, suppose from the business datum of another user B and also can pass through modulation module 220, the mapping that information code element decomposing module 222 and SC-SFHP channel Mapping module 224 are finished designate sub.Suppose that above-mentioned data are mapped among the identical TFC, these data can be imported into to cut and finish quadrature in the general level accumulator module 226 and add up (dotted line is represented).For up (travelling carriage is to the base station) transfer of data, in the travelling carriage transmitter, will carry out the code channel stack to the SC-SFHP channel of distributing to this travelling carriage.After the disposing of above business datum, can with other channel informations, be imported into IFFT module 228 in the ofdm system together as the information of control channel, finish conversion from frequency domain to time domain.Transmit by ofdm system afterwards.

Shown in Figure 3 is the time-frequency distribution schematic diagram of the orthogonal spectrum expansion SC-SFHP channel of VSFH-OTFCDM.In this example, TFC is made up of a plurality of subcarrier in frequency domain.From time shaft, divide the business/control channel part that comprises training sequence 34 and form by function by the SC-SFHP channel; From the frequency domain axle, in available subchannel, comprise a plurality of TFC pieces 36.In the sign indicating number territory, a plurality of SC-SFHP channels 32 with identical frequency hopping pattern can be in the stack of sign indicating number territory, because the SC-SFHP channel Mapping is in the TFC of different time domain, so the period of time T of SC-SFHP channel _SC-SFHPWill be by the time cycle decision of the TFC of these time domains.

Shown in Figure 4 is the signal model of VSFH-OTFCDM.At transmitter 40, signal is via modulation module 402 back orthogonal spectrum expansions, and orthogonal spectrum expansion is by 404 expressions of multiplier module, and afterwards, the signal behind the orthogonal spectrum expansion can be finished the signal in orthogonal stack by adder module 406, and is mapped to time-frequency domain.Signal is by channel module 408 afterwards.In receiver 42, signal can carry out channel equalization 410 at frequency domain, and wherein estimated channel information is provided by channel estimation module 412; Can recover orthogonal signalling by multiplier module 414 through equalized received signal, and deliver to demodulation module 416 subsequently and carry out demodulation.Under this model, suppose modulation signal M _iExpression, total N SC-SFHP channel stack.Suppose that the quadrature code length is Q, the orthogonal code S of i SC-SFHP channel _i={ S _{I, 1}, S _{I, 2}..., S _{I, Q}Expression; Frequency domain channel represents that with H the estimated channel parameter is used Expression.

T is the cumulative signal at frequency domain, and with formula (1) expression, j is corresponding subcarrier number in the formula.

$T_j=\begin{array}{cc}\underset{i=1}{\mathrm{\Σ}}{M}_i{S}_{i,j}& j=1,\·\·\·,Q\end{array}---\left(1\right)$

R _jFor being the received signal of j, with formula (2) expression in subcarrier number

R _j＝T _j*H _j j＝1，...，Q (2)

Formula (3) has been represented the process of and despreading balanced to orthogonal code, wherein S _PIt is the orthogonal code sequence of i SC-SFHP channel

$\stackrel{-}{M_i}=\underset{j=1}{\overset{Q}{\mathrm{\Σ}}}\frac{R_j}{\stackrel{-}{H}j}*S_{p,j}---\left(3\right)$

Signaling channel is estimated as inclined to one side, and inclined to one side estimated channel parameter is then arranged

Available formula (4) expression

H _j＝H _j*δ _j (4)

To can get in expression formula (4) substitution (3):

${\stackrel{-}{M}}_i=\underset{j=1}{\overset{Q}{\mathrm{\Σ}}}\frac{R_j}{(H_j*{\mathrm{\δ}}_j)}*S_{p,j}=\underset{j=1}{\overset{Q}{\mathrm{\Σ}}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\frac{M_i}{{\mathrm{\δ}}_j}(S_{i,j}*S_{p,j})---\left(5\right)$

When the estimated bias for the channel that is experienced of an orthogonal code is same value δ, following formula can be expressed as:

${\stackrel{-}{M}}_i=\frac{1}{\mathrm{\δ}}\underset{j=1}{\overset{Q}{\mathrm{\Σ}}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{M}_i(S_{i,j}*S_{p,j})---\left(6\right)$

Then work as S _i=S _P,

$M_i=\frac{1}{\mathrm{\δ}}{M}_i---\left(7\right)$

As mentioned above, to VSFH-OTFCDM quadrature decoder influence be the deviation of channel estimating, when having only the estimated bias unanimity when a channel that orthogonal code experienced, just easily guarantee the orthogonality of orthogonal code.And the orthogonal spectrum expansion under frequency selective fading channels, its systematic function will be trading off under diversity effect and orthogonality keep.By above analysis as can be known, in the VSFH-OTFCDM system, the orthogonal spectrum expansion information of controlling via VSF is assigned in the SC-SFHP channel, and the selection of TFC is by the frequency hopping pattern decision of selecting in the SC-SFHP channel.Then corresponding certain orthogonal code, it both distributed and can also can as long as the channel estimation bias variation is little, still be easy to the orthogonal property that receiving terminal recovers quadrature decoder at incoherent frequency domain in relevant frequency domain at frequency domain.In the VSFH-OTFCDM system, the selection of frequency hopping pattern can make orthogonal spectrum expansion information to distribute in coherence time and relevant frequency domain, also can distribute at incoherent frequency domain and irrelevant time-domain.

Embodiment

Below TFC of supposition has 8 subcarriers, and a SC-SFHP is made up of 8 TFC, and the composition of TFC is controlled by frequency hopping pattern among the SC-SFHP, and data message is by variable bandspread factor VSF control, and variable bandspread factor VSF size can be 1,2 ..., 64.Orthogonal spectrum expansion is in the SC-SFHP channel.In this case, same subscriber can be distributed to, also different user can be distributed to by the same time frequency unit group of frequency hopping pattern control.These users can adopt identical spreading factor, and the orthogonal code of the same spread factor is selected from the brother of node in the orthogonal code structure tree.Example is as shown in table 1, has adopted identical spreading factor in the same time frequency unit group.When VSF was 2, system supported 2 quadrature code channels in the time frequency unit of correspondence, also the SC-SFHP number of channel M of the maximum of promptly supporting in same time frequency unit _Max-num=2, the modulating data symbol signal that can carry in the SC-SFHP channel is counted N _SC-SFHP-cm=32.Then in this time frequency unit group, but maximum information transmitted code element number is N _SC-SFHP-cm* M _Max-num=64.

VSFH-OFCDM is same to support to abide by the signal of different spreading factor SF of certain specification in the stack of same time frequency unit group.When superposeing when adopting different VSF spreading factor, be to guarantee orthogonality, the selection of the orthogonal code of different spreading factor SF should come different father node in the self-orthogonal code structure tree.As shown in Figure 5, can adopt and be numbered 1,2, the orthogonal code of 5 different spreading factor SF, the data number 8+16+32=56 that can transmit.Also can adopt and be numbered 1,2, the orthogonal code of 4,5 different spreading factor SF, the data number that can transmit is 64.Therefore, total data number that transmits is smaller or equal to 64.

In order to safeguard the orthogonality of orthogonal code, if in same time frequency unit group, select different SF for use, then adopt in all time-frequency subcarriers that need to fill behind the orthogonal code spread spectrum of these different SF in this time frequency unit group, but because SC-SFHP is minimum allocation units, taken the part of a SC-SFHP channel when the business datum that adopts certain SF, especially for the channel that hangs down SF, also need fill whole SC-SFHP channel even without remaining data, this will cause the certain system resource waste and the increase in processing time.And the waste of this resource is more outstanding for the situation of different SF.

Table 1. adopts SC-SFHP channel parameter under the identical spreading factor

VSF factor	N SC-SFHP-cmThe modulating data symbol signal number that can carry in=SC-SFHP the channel	M max-numThe SC-SFHP number of channel of=maximum in same time frequency unit, supported
			1	64	1
2	32	2
			4	16	4
8	8	8
			16	4	16
32	2	32
			64	1	64

Claims (9)

1. CDMA access method based on the quadrature time-frequency domain of variable spread spectrum and frequency hopping comprises step:

A), select suitable time frequency unit group at the time-frequency domain of orthogonal frequency division multiplex OFDM according to frequency hopping pattern;

B) from orthogonal code sets, select orthogonal code, in the OFDM time frequency unit group selected, adopt orthogonal spectrum expansion to determine the subchannel under the selected frequency hopping pattern by step a);

C) in group selected from step a), carry out multiplexing to the spread spectrum information in the subchannel SC-SFHP channel under the selected frequency hopping pattern of in identical time frequency unit group, from step b), selecting that satisfies orthogonal property with identical time frequency unit;

D) from step c), obtain multiplexing after data message carry out transfer of data by ofdm system.

2. in accordance with the method for claim 1, it is characterized in that the same time frequency unit group of described frequency hopping pattern control can be distributed to same subscriber and also can distribute to different user.

3. in accordance with the method for claim 1, it is characterized in that, described SC-SFHP channel is made up of a plurality of time frequency unit, each time frequency unit is made up of more than or equal to 1 frequency domain continuous sub-carriers one group of number, and the subcarrier combination mode in the time frequency unit can be frequency domain continuous sub-carriers combination or make up by the index of subcarrier.

4. in accordance with the method for claim 1, it is characterized in that the described SC-SFHP channel that superposes can adopt identical spreading factor or different spreading factors in the same time frequency unit group by frequency hopping pattern control.

5. in accordance with the method for claim 1, it is characterized in that in the multiplexing SC-SFHP channel, the orthogonal code of the same spread factor is selected from the brother of node in the orthogonal code structure tree in the same time frequency unit group by frequency hopping pattern control.

6. in accordance with the method for claim 1, it is characterized in that in the described SC-SFHP channel multiplexing in the same time frequency unit group by frequency hopping pattern control, the selection of the orthogonal code of different VSF spreading factors comes different father node in the self-orthogonal code structure tree.

7. one kind is utilized orthogonal spectrum expansion and frequency hopping to control the emitter that multichannel is divided in ofdm system, comprising:

The information code element decomposing module is used for user profile is decomposed subchannel SC-SFHP channel under each selected frequency hopping pattern;

The orthogonal spectrum expansion module is used for the user profile that spread spectrum is imported, and spread spectrum information is mapped to SC-SFHP channel Mapping module;

SC-SFHP channel Mapping module is used to shine upon information behind the spread spectrum to the SC-SFHP channel;

Frequency hopping pattern module and change spreading factor module are used at the described SC-SFHP channel of the common control of time-frequency domain;

The TFC mapping block is used to finish information after the SC-SFHP channel Mapping to the mapping of designate sub;

Cut general level laminating module, the SC-SFHP sub-channel signal that will have identical time-frequency domain distribution superposes, and the signal that will cut after the general level stack transmits by ofdm system.

8. according to the described device of claim 7, it is characterized in that the same time frequency unit group of described frequency hopping pattern module controls can be distributed to same subscriber, also can distribute to different user.

9. according to the described device of claim 8, it is characterized in that the described SC-SFHP channel that superposes can adopt identical spreading factor or different spreading factors in the same time frequency unit group by the frequency hopping pattern module controls.

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