text: Patent US6069883 - Code division multiple access system providing enhanced load and ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA code division multiple access system method and apparatus provides for allocation of increased bandwidth to a requesting mobile station. An access controller receives a data burst request (from either a requesting mobile station or from an external network already in connection with the mobile station)...http://www.google.com/patents/US6069883?utm_source=gb-gplus-sharePatent US6069883 - Code division multiple access system providing enhanced load and interference based demand assignment service to usersAdvanced Patent SearchPublication numberUS6069883 APublication typeGrantApplication numberUS 08/841,980Publication dateMay 30, 2000Filing dateApr 8, 1997Priority dateOct 5, 1995Fee statusPaidAlso published asCA2184772A1, CA2184772C, EP0767548A2, EP0767548A3, US5734646, US6088335Publication number08841980, 841980, US 6069883 A, US 6069883A, US-A-6069883, US6069883 A, US6069883AInventorsRichard Paul Ejzak, Chih-Lin I, Douglas Knisely, Sarath Kumar, Subhasis Laha, Sanjiv NandaOriginal AssigneeLucent Technologies IncExport CitationBiBTeX, EndNote, RefManPatent Citations (3), Referenced by (118), Classifications (18), Legal Events (7) External Links: USPTO, USPTO Assignment, EspacenetCode division multiple access system providing enhanced load and interference based demand assignment service to usersUS 6069883 AAbstract A code division multiple access system method and apparatus provides for allocation of increased bandwidth to a requesting mobile station. An access controller receives a data burst request (from either a requesting mobile station or from an external network already in connection with the mobile station) requesting a first data rate in excess of the basic data rate B allocated to a mobile station of a first cell. The access controller determines an increased data rate which is to be granted to said mobile station without causing excessive interference at said first cell and at least one adjacent cell and transmits a data burst assignment to a base station of said first cell indicating the increased data rate which has been granted to said mobile station. In another feature, the access controller processes a data burst request received from a mobile station involved in a soft handoff between multiple base stations and negotiates with those base stations for an increased data rate which may be granted to the requesting mobile station. One feature enables additional interactions to further refine the allocation process. A variety of system architectures are also described.
  We claim: 1. In a code division multiple access system including an access controller and multiple cells, each cell having a base station and multiple mobile stations, a method of allocating bandwidth to a mobile station comprising the steps of:at the access controller, receiving a data burst request requesting a first data rate in excess of the basic data rate B allocated to a mobile station of a first cell, determining an increased data rate which is to be granted to said mobile station without causing excessive interference at said first cell and at least one adjacent cell; and transmitting a data burst assignment to a base station of said first cell indicating the increased data rate which has been granted to said mobile station. 2. The method of claim 1 wherein the data burst request is a request received from said mobile station requesting an increased data rate over a basic data rate for a reverse link connection to the base station of said first cell.
  REFERENCE TO PARENT APPLICATION This is a continuation-in-part of application Ser. No. 08/539,476, filed Oct. 5, 1995 now U.S. Pat. No. 5,734,646.
  BACKGROUND OF THE INVENTION The advantages of code division multiple access (CDMA) for cellular voice have become well known. In spite of the advantages, conventional CDMA systems have very limited per user throughput and are not well suited to "bandwidth on demand" local area network (LAN)-like applications. In fact, current CDMA standards operate in circuit mode, assume a homogeneous user population, and limit each user to a rate which is a small fraction of the system capacity. As mentioned above, CDMA relies on the averaging effect of the interference from a large number of low-rate (voice or circuit-mode data) users. It relies heavily on sophisticated power control to ensure that the average interference from all users from an adjacent cell is a small fraction of the interference from the users within a cell. The imperfect power control in a homogeneous system has a direct impact on system performance.
  SUMMARY OF THE INVENTION Our inventive Load and Interference based Demand Assignment (LIDA) techniques protect voice (and other high priority or delay sensitive) isochronous users while accommodating the peak data rate needs of high data rate users when the load on the system permits. More particularly, our method and apparatus provides a code division multiple access (CDMA) system, including an access controller and plurality of cells each having a base station and multiple mobile stations, with a way of allocating bandwidth to a mobile station. The access controller receives a data burst request (from either a requesting mobile station or from a network, external to the system, already in connection with the mobile station) requesting a first data rate in excess of the basic data rate B allocated to a mobile station of a first cell. The access controller determines an increased data rate which is to be granted to said mobile station without causing excessive interference at said first cell and at least one adjacent cell and transmits a data burst assignment to a base station of said first cell indicating the increased data rate which has been granted to said mobile station.
  GENERAL DESCRIPTION To curtail the potentially large interference variation in cellular CDMA systems serving mixed traffic, the present invention incorporates autonomous and/or coordinated network access control that accounts for channel loading and interference. It dynamically assigns higher data rates to users while simultaneously adjusting the Quality of Service (QOS) for each user according to service requirements. Higher data rates are assigned to users by either permitting users to transmit on multiple channels simultaneously or by using other means, such as variable spreading gains, variable channel coding rate, variable chip rate, varying the modulation (Walsh modulation, coded modulations, BPSK, QPSK . . . ) etc. An elegant scheme that achieves this is Multi-Code CDMA (MC-CDMA) with dynamic demand assignment, described in U.S. Pat. No. 5,442,625 entitled "Code Division Multiple Access System Providing Variable Data Rate Access" which issued on Aug. 15, 1995 to Richard D. Gitlin and Chih-Lin I. The QOS is adjusted through the power control with a target Frame Error Rate (FER) and signal to interference ratio (E.sub.b /N.sub.0) on the channel. In this invention, the network uses a control strategy that accounts for channel loading, interference, and soft handoff in making the rate assignment and QOS decisions. It ensures priority for voice users, if so desired. Thus, dynamic, packet-like demand-assigned access enables users with different services to access the channel at desired rates and QOS requirements.
  Radio distance is the effective radio loss that a signal, transmitted from a base station, incurs in transit to a mobile station. The received pilot power Pi at a mobile station is then P/z.sub.i, where P is the transmitted pilot power from each base station and z.sub.i is the effective "radio distance." As a mobile station MS1.1 in cell 100 approaches cell 120, the power level of the received pilot from base station BS2 increases beyond a threshold, T.sub.add, and the mobile station will enter "soft handoff." During soft handoff, the mobile station communicates with both base stations BS1 and BS2. We extend the use of the pilot measurement to burst access control in this invention.
  The serial-to-parallel station 281 converts a user's serial digital information input, which may be up to M.sub.max times the basic source rate B (where M.sub.max streams (where M is an integer≦M.sub.max) The basic rate B is also referrred to herein as a data rate unit. The outputs of S/P station 281 connect to code spreaders 204, 224, and 244, which spread each of the M data streams, respectively, into a channel bit rate using codes C.sub.1, C.sub.2, and C.sub.M which are unique to user 1. The combiner 254 combines the output of code spreaders 204, 224 and 244. The output signal combiner 254 is coupled to coders 205 and 206. In coder 205, an in-phase code A.sub.1 further encodes the signal from combiner 254. Similarly, coder 206 further encodes the signal from combiner 254 using a quadrature-phase code A.sub.Q. The codes A.sub.1 and A.sub.Q are common to all mobile stations of FIG. 1.
  The output of coder 205 is used to modulate the carrier signal Cosω.sub.c t in modulator 208. The output of coder 206 is used to modulate the carrier signal Sinω.sub.c t in modulator 209. In certain applications, an optional delay station 207 may be utilized to provide better spectral shaping. The output of modulators 208 and 209 are radio frequency signals which are combined in combiner 210 and transmitted via antenna 211 over the air to a base station (e.g., BS1 of FIG. 1).
  A base station (e.g., BS1) transmits at a different carrier frequency which is received and decoded by mobile stations MS1.1-MS1.N within its cell site 100. In our illustrative example, receiver 260 of mobile station MS1.1 includes a demodulator (not shown) to demodulate the carrier frequency to obtain a channel bit rate signal which is decoded using codes A.sub.1 and A.sub.Q and then de-spread using the associated code sequence C.sub.1 to obtain the information data signal to be outputted to user 1.
  The base station, e.g., BS1, operates in a similar manner to receiver 260 of mobile station MS1.1 to receive, decode and de-spread the user 1 information data signal. Similarly, the other mobile stations, illustratively represented by mobile station MS1.N, operate in the same manner as mobile station MS1.1, except that user N has a unique code C.sub.N to distinguish it from user 1. In mobile station MS1.N, the in-phase and quadrature codes A.sub.1 and A.sub.Q, respectively, as well as the carrier frequency f.sub.c are the same as those used for mobile station MS1.1.
  I.sub.0 =αN(1+γ)                               (1)
  where α is the speech activity factor. We use the nominal interference, I.sub.0, in a voice-only system with a capacity of N users per cell, as the reference QOS in the subsequent discussion.
  The impact on out-of-cell interference is considered next. In the voice-only system, where voice users are uniformly distributed in the cells 110-160, most of the out-of-cell interference comes from the users in other cells (e.g., MS2.1) that are near the cell boundaries 111-161. Due to the large path loss exponent, users further away from the boundary (e.g., MS2.N) contribute little to out-of-cell interference. As the high data rate user (e.g., MS1.1), transmitting at M/α times the average data rate of a voice user, moves along path 101 closer to the boundary 121, the in-cell interference to BS1 remains at around M/α while the out-of-cell interference to BS2, caused by the high rate data user, rapidly rises beyond what was computed for the voice system. However, to maintain the required Quality of Service (QOS), the total interference at each cell must be controlled to be no more than I.sub.0.
  To quantify our discussion above, assume there are N.sub.v voice users per cell and one active (transmitting) high rate data user in the host cell, the total interference in the host cell and in the closest neighboring cell (with respect to that data user) can be expressed as follows:
  I.sub.d (r)=αN.sub.v (1+γ)+Mγ.sub.d (r), (2)
  where `r` is the distance from the active high rate data to its host cell site. γ.sub.d (r)=1 for the host cell since it is power controlled by that cell and γ.sub.d (r)≈(2R-r).sup.4 /r.sup.4 for the neighboring cell it approaches, where R is the cell radius. The access control mechanism for high rate data users must satisfy the constraint:
  I.sub.d (r)≦I.sub.0                                 (3)
  in both the host cell and the approached neighboring cell. We will seek to adjust N.sub.v, the number of voice users, or M, the multiple of the basic data rate B being used by the data user, as a function of `r`, in order to meet the interference constraints. The issues and our strategies are elaborated in the next sections.
  In the above discussion, the out-of cell interference due to a data user is a function of (2R-r)/r. Hence, the access controller should use the knowledge of the distance of the mobile from the cell site to determine permitted values of N.sub.v and M. There are two issues with using `r` as the control variable. First, the distance of the mobile from the cell site cannot be determined accurately. More importantly, although the discussion of out-of-cell interference above is in terms of the distance `r`, the actual interference is strongly dependent on the shadow fading conditions in addition to the distance. Hence, control based on geographic distance is neither optimal nor practical. The present invention uses a control based on radio distance, using pilot strength measurements to address both issues. This solution can easily be an integral part of a CDMA system.
  In current CDMA systems, mobile assisted soft handoff is implemented as follows. The base station provides the mobile with a neighbor list of pilots. The mobile periodically measures the pilot strength on its neighbor list and transmits it to the cell site. If the pilot strength of a base station to which the mobile is not connected is greater than a threshold T.sub.add, the base station initiates a soft handoff for the mobile. The present invention extends the concept of using pilot strength measurements for soft handoff decisions to using it for access control of high data rate users.
  As shown in step 405, each user is assigned a unique primary code, i.e., C.sub.1, determined as the user-specific PN sequence. When a user is quiescent, 407, a very low rate (say, eighth rate) (sub-rate) signaling channel is maintained using its primary code. This sub-rate channel helps in maintaining synchronization and coarse power control. It is maintained whether the user is "connected" to one base station or is in soft handoff with multiple cells. Since the transmission during eighth rate frames is intermittent, both the synchronization and the power control are inadequate if the quiescent period is long.
  Specifically, in the presence of shadow fading, the average interference at the cell site for the basic voice-only system is modified from Equation 1 as described in the article by K. S. Gilhousen et al. entitled "On the Capacity of a Cellular CDMA System" (IEEE Trans.Veh. Technol, Vol. VT-40, No. 2, May 1991, pages 303-312). Let us denote it as I.sub.0.sup.s =αN(1+γ.sup.s, where γ.sup.s is the average out-of-cell interference in the presence of shadow fading. Similarly, in an integrated voice and data system, the interference factor for a data user in a neighboring cell is γ.sub.d.sup.s (z.sub.1,z.sub.2)=z.sub.1 /z.sub.2, where z.sub.1 and z.sub.2 are the path loss of the mobile to the host cell and the neighboring cell, respectively. Note that γ.sub.d.sup.s (z.sub.1,z.sub.2)=1 in the case of the host cell because of power control. The path loss (radio distance) z.sub.1 and z.sub.2 include the distance loss component as well as the shadow fading component. The interference constraint becomes:
  I.sub.d.sup.s (z.sub.1,z.sub.2)=αN.sub.v (1+γ.sup.s)+Mγ.sub.d.sup.s (z.sub.1,z.sub.2)≦I.sub.0.sup.s.                   (4)
  The values z.sub.i and z.sub.2 are derived from the pilot strength measurements.
  With reference to FIGS. 4 and 6, we describe one embodiment of our autonomous access control feature of the present invention. As described in step 411 above, the mobile station provides pilot strength measurements in the access request. If the host's load condition is too close to a predetermined load level, step 600, then a retry delay command is sent, in step 600a. If the host load condition permits a burst access, but the mobile is in a soft handoff, step 601, then the access controller limits the mobile to the basic data rate B (i.e., multiplier m=1). The burst assignment message, step 605, permitting a data rate of m times the basic rate B is sent to the requesting mobile. If the host load condition permits burst access and the mobile is not in soft handoff, then step 607 is performed. In step 607, the base station pilot strength measurements for all neighbors, `i`, are determined. The pilot strength measurement P/z.sub.i (PMRM of 411) is formed for all base stations `i` in the neighbor list, where P is the known transmission power level of the base stations and z.sub.i is the path loss or radio distance. If P/z.sub.i is below a high rate data access threshold T.sub.hra, it indicates that the mobile will not cause any excess interference to neighbor base stations and the mobile is permitted (step 609) to transmit a rate which is the minimum of the requested multiple M or the maximum multiple M.sub.R. (The mobile and the base station can locally generate the M codes needed for the multiple rate transmissions using subcode concatenation in MC-CDMA as described in the previously referenced patent. A new method for the moble station and the base stations to generate multiple PN sequence masks for multiple reverse channels is described here in the section on Reverse Link Channels.) In step 605, the access controller sends the burst assignment message to the requesting mobile.
  The threshold T.sub.hra is chosen such that the total interference received from a requesting mobile at any neighbor base station is less than I.sub.0. Note that to accommodate high rate data users the system may limit the number of voice users N.sub.v to be smaller than the maximum permissible in a voice-only system. There is a tradeoff between raising T.sub.hra and increasing N.sub.v, the number of voice users per cell.
  If any one of the neighbor base station pilot strengths (P/z.sub.i) in step 607 is determined to be higher than the threshold T.sub.hra, the mobile is permitted only to transmit at the basic rate B, step 603. High rate access will not be allowed for the requesting mobile until all neighbor base station pilot strengths are found to be below T.sub.hra. Note that the soft handoff decisions are made separately. The soft handoff add and drop thresholds T.sub.add and T.sub.drop will typically be larger than the high rate data access threshold T.sub.hra. Consequently, as previously discussed in step 601, mobiles in soft handoff will only be allowed to transmit at the basic rate B (i.e., m=1). Conversely, any transmission at basic rate B requires no demand assignment.
  With reference to FIG. 7, we describe our enhanced autonomous access control feature. The previously described autonomous access control permits only two selection data rates, namely a basic rate (m=1, step 603) and a high rate, which is the minimum of the requested rate M or the system's maximum rate M.sub.R (step 609). The enhanced autonomous access control feature creates multiple thresholds which increase the coverage area for higher rate data users such that rates two, three, . . . times (even non-integer multiples) higher than the basic rate B can be assigned. Thus, data users requesting higher data rates are usually assigned a higher data rate when they are more centrally located in their cell and assigned succeedingly lower data rates as they approach a cell boundary.
  In steps 700 and 700a, the host cell's load condition check is performed in the same manner as in steps 600 and 600a. If the mobile (e.g., MS1.1) is in soft handoff, then step 703 and step 705 are performed in the same manner as steps 603 and 605. However, if the mobile is not in soft handoff, then the access controller selects a data rate using step 707. In step 707, the maximum pilot strength P/z.sub.i from all base stations `i` in the neighborhood is determined from the set of pilot strength measurements reported by mobile MS1.1, in step 411. The access controller compares the maximum pilot strength with a set of thresholds {T.sub.m, m=0, 1, . . . M.sub.R }, where T.sub.m >T.sub.m+1, as shown in FIG. 10. Each threshold T.sub.m corresponds to a different permitted data rate multiple m. For consistency, T.sub.0 =P and T.sub.Mr =T.sub.hra. If any neighbor's pilot strength P/z.sub.i is not below the threshold T.sub.1, then the mobile MS1.1 is permitted by its base station BS1 only to access the basic rate B (m=1), as shown in step 703. If the maximum of pilot strength P/z.sub.i is between T.sub.m and T.sub.m-1, then the data rate multiple m is selected as shown in FIG. 10, so that the interference at any neighbor cell's base station is less than I.sub.0. Again, in step 709, the access controller selects the data rate multiple m to be no greater than the system limit M.sub.R and the requested multiple M. In step 705, the burst assignment message 503 includes the rate multiple m. As before, the base station checks its list of scheduled bursts and adds the mobile to its request list, if the list is shorter than L frames, and transmits the assignment message 415 to the mobile. If the scheduled list is longer than the threshold L, the mobile is told in message 415 to retry later.
  On the other hand, if in step 707 any neighbor's pilot strength is above the T.sub.1 threshold, then it means that a high rate transmission from that mobile MS1.1 may cause excessive interference in that neighbor's cell. Consequently, the mobile is restricted to the base rate (m=1) as shown in step 703.
  αN.sub.v (1+γ.sup.s)+mγ.sub.d.sup.s (z.sub.1,z.sub.2)≦I.sub.0.sup.s,                   (5)
  where γ.sub.d.sup.s (z.sub.1,z.sub.2)=1 for the host cell. Thresholds {T.sub.m are defined to satisfy Equation 5 for bit rate multiples m=1, 2, . . . ; up to M.sub.R. Again, mobiles in soft handoff will be only allowed to transmit at basic rate (m=1); which requires no extra negotiations among cells involved in the handoff.
  With reference to FIG. 8, we describe our neighbor coordinated access control feature. Neither of the schemes above account for instantaneous loading in the neighbor cells. As discussed in the following paragraphs, light loading in neighbor cells can be exploited to permit higher rate access while still meeting the interference constraint I.sub.O.sup.s.
  When a mobile MS1.1 is connected to a single base station BS1, the rate assignment decision in response to a high data rate access request, 411, is facilitated if the load at the neighbor cells is known, 802, to the base station BS1. In step 803, the base station computes the mean load N.sub.v. In step 805, instead of fixed thresholds, the base station BS1 makes rate assignment decisions by determining the smallest `m` that satisfies the following inequality for all neighbor base stations and itself:
  α(N.sub.v.sup.i +N.sub.v γ.sup.s)+mγ.sub.d.sup.s (z.sub.1,z.sub.i)≦I.sub.0.sup.s,                   (6)
  where N.sub.v is the average number of voice users per cell in the neighborhood, N.sub.v.sup.i is the number of voice calls in cell `i` and z.sub.i is the "radio distance" of the data user to base station of cell `i` , where `i` is the index of the neighbor list. The host cell corresponds to i=1. Actually, for each neighbor cell, the value N.sub.v.sup.i should be considered as the "load in terms of equivalent" voice calls. By choosing the smallest `m` that satisfies Equation 6 (step 805) for all neighbor cells `i`, we ensure that the admission of a burst at `m` times the basic rate B will not cause excessive interference at any neighbor. In this case, the only communication required is for the neighbor cells to periodically provide updates, step 802, of their current load. In step 807, the multiple `m` is selected to be the minimum of m.sub.i, M and M.sub.R. In step 809, if the mobile is not in soft handoff, then, as before, if the scheduled list is shorter than L frames, the rate assignment and burst parameters are provided to the mobile, step 811; otherwise, the mobile is told in step 811 to retry.
  If the basic channel is the only one used for power control on the reverse link, then using the power level determined to transmit partial rates to control full rate transmissions on the other channels is not acceptable. This implies that only full rate must be transmitted on the basic channel during multiple channel transmissions. (That is, 2 4 2.5.times., 3.25.times., etc.). This restriction appears to be reasonable. Also, the same reasoning applies to the forward link, but not as strongly.
  SUMMARY When the present invention is implemented as a MC-CDMA system with LIDA, it offers the following features:
  It sacrifices (some) Forward Error Correction (FEC) in favor of retransmission using ARQ to reduce E.sub.b /N.sub.0 requirement, and increase capacity.
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service support over 802.16 air interface* Cited by examinerClassifications U.S. Classification370/335, 370/441, 370/468, 370/342International ClassificationH04L12/28, H04J13/04, H04L12/56, H04B7/26, H04W72/08, H04W16/14, H04W28/22, H04W74/00, H04W36/18Cooperative ClassificationH04B2201/70703, H04W72/082, H04W36/18, H04W28/22European ClassificationH04W28/22Legal EventsDateCodeEventDescriptionMar 7, 2013ASAssignmentFree format text: SECURITY INTEREST;ASSIGNOR:ALCATEL-LUCENT USA INC.;REEL/FRAME:030510/0627Owner name: CREDIT SUISSE AG, NEW YORKEffective date: 20130130Sep 23, 2011FPAYFee paymentYear of fee payment: 12Sep 25, 2007FPAYFee paymentYear of fee payment: 8Dec 6, 2006ASAssignmentOwner name: LUCENT TECHNOLOGIES INC., NEW JERSEYFree format text: TERMINATION AND RELEASE OF SECURITY INTEREST IN PATENT RIGHTS;ASSIGNOR:JPMORGAN CHASE BANK, N.A. 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