WO2011041926A1

WO2011041926A1 - Signaling of random access channel load indicator bits

Info

Publication number: WO2011041926A1
Application number: PCT/CN2009/074362
Authority: WO
Inventors: Jian Feng Qiang; Peter Skov; Juha S. Korhonen
Original assignee: Nokia Corporation
Priority date: 2009-10-08
Filing date: 2009-10-08
Publication date: 2011-04-14

Abstract

A method includes receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of the plurality of component carriers. The method further includes selecting a random access channel based at least in part on the received load indications, and transmitting on the selected random access channel.

Description

SIGNALING OF RANDOM ACCESS CHANNEL LOAD INDICATOR BITS

TECHNICAL FIELD:

The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to control and management of random access channels between a network access node, such as an eNB, and a user device or user equipment (UE).

BACKGROUND:

This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3GPP third generation partnership project

ACK acknowledge

BCH broadcast channel

BW bandwidth

C-plane control plane

CC component carrier

CN core network

DL downlink (eNB towards UE)

DRX discontinuous reception

eNB EUTRAN Node B (evolved Node B)

EPC evolved packet core

EUTRAN evolved UTRAN (LTE) HSPA high speed packet access

LTE long term evolution

MAC medium access control

MM/MME mobility management/mobility management entity

NAS non-access stratum

Node B base station

OFDMA orthogonal frequency division multiple access

O&M operations and maintenance

PDCP packet data convergence protocol

PHY physical

PUCCH physical uplink control channel

QoS quality of service

RACH random access channel

RAN radio access network

RLC radio link control

RRC radio resource control

RRM radio resource management

SGW serving gateway

SC-FDMA single carrier, frequency division multiple access

SON self-optimization network

TDD time division duplex

UE user equipment

UL uplink (UE towards eNB)

UMTS universal mobile telecommunication system

UTRAN universal terrestrial radio access network

The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as EUTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.

One specification of interest is 3GPP TS 36.300, V8.7.0 (2008-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8). This system may be referred to for convenience as LTE Rel-8, or simply as Rel-8. In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Release 8 LTE system.

Figure 1 reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/M AC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an SI interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a SI MME interface and to a Serving Gateway (SGW) by means of a SI interface. The SI interface supports a many to many relationship between MMEs / Serving Gateways and eNBs.

The eNB hosts the following functions:

functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);

IP header compression and encryption of the user data stream;

selection of a MME at UE attachment;

routing of User Plane data towards Serving Gateway;

scheduling and transmission of paging messages (originated from the MME);

scheduling and transmission of broadcast information (originated from the MME or

O&M); and

measurement and measurement reporting configurations to provide mobility and scheduling.

Of particular interest herein are the further releases of 3GPP LTE targeted towards future IMT-A systems, referred to herein for convenience simply as LTE-Advanced (LTE-A).

Reference can be made to 3GPP TR 36.814, Vl.2.1 (2009-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Further Advancements for E-UTRA Physical Layer Aspects (Release 9), incorporated by reference herein in its entirety. Reference can also be made to 3GPP TR 36.913, V8.0.1 (2009-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8), also incorporated by reference herein in its entirety. A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost.

In LTE Rel-8 (and Rel-9) the RACH procedure plays an important role in RRC connection setup, RRC connection wakeup after a long DRX period, and in a handover procedure. The RACH is characterized by a limited amount of control information a risk of collision. Normal DL/UL transmission can take place after the RACH procedure(s) are completed.

The RACH procedure is performed for the following five events in the LTE system: 1. Initial access from RRCJDLE;

2. RRC Connection Re-establishment procedure;

3. Handover;

4. DL data arrival during RRC_CONNECTED requiring a random access procedure; e.g., when UL synchronization status is "non-synchronized"; and

5. UL data arrival during RRC_CONNECTED requiring random access procedure; e.g., when UL synchronization status is "non-synchronized", or there are no PUCCH resources for SR available.

In general, the random access procedure takes two distinct forms:

a) contention based (applicable to all five of the foregoing events); and

b) non-contention based (applicable to only handover and DL data arrival). General reference to RACH, both contention based and non-contention based, for Rel-8 and Rel-9 can be found in Section 10.1.5, "Random Access Procedure", of 3GPP TS 36.300 V8.8.0 (2009-03) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), and in 3GPP TS 36.300 V9.0.0 (2009-06) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 9), respectively.

The random access procedure can become a bottleneck in a reduced RRC states scenario (there are only two RRC states: RRC-idle and RRC-connected) in the LTE Rel-8 system. The RACH is the only mechanism to transition from the RRC-idle to the RRC-connected states (of reactive UEs). As a result, the RACH load from initial access and RRC connection re-establishment is large. Further, the response time of the RACH procedure in LTE is more stringent than previous systems, such as UMTS, as the end-to-end delay requirement is more stringent than that of UMTS.

The number of users can exceed 200,000 in a 500m cell (e.g., see R2-062923, "C-RNTI length in LTE", NTT DoCoMo). By a fairly modest estimation as many as 7,000 UEs may be camping in the 10MHz system (e.g., see R2-070205, "LTE cell load / RACH load estimations", Samsung). The asynchronous RACH (aRACH) load is handled with random preambles, and a large load is handled with dedicated preambles. Figure 3 shows both the aRACH load and the dedicated preamble load for "normal (RACH load)", "possible (RACH load)" and "rare (rarely high load)" situations, and reproduces Figure 2 of R2-070205. According to R2-070206, "Collision probability on RACH", Samsung, it is a requirement to not use random signatures in target cells at handover in order to have the aRACH resource usage within acceptable limits. The total number of PRACH preamble sequences is a maximum of 64 per cell in the LTE system. The desired preamble collision probability could typically be around 1%, meaning that the average RACH load should be less than one random signature per a set of 64 signatures. Thus, even if one were to use dedicated signatures for handovers and LTE_ACTIVE DL transmission continuation, the available PRACH preamble resources will be critical when compared with the possible RACH load in a LTE cell.

As specified in 3GPP TR 36.913, LTE-A should operate in spectrum allocations of different sizes, including wider spectrum allocations than those of Rel-8 LTE, e.g., up to 100MHz, to achieve the peak data rate of lOOMbit/s for high mobility and 1 Gbit/s for low mobility. It has been agreed that carrier aggregation is considered for LTE-A in order to support bandwidths larger than 20 MHz.

As is stated, carrier aggregation, where two or more component carriers (CC) are aggregated, is considered for LTE- Advanced in order to support transmission bandwidths larger than 20DMHz. The carrier aggregation could be contiguous or non-contiguous.

A terminal may simultaneously receive one or multiple component carriers depending on its capabilities. An LTE-Advanced terminal with reception capability beyond 20 MHz can simultaneously receive transmissions on multiple component carriers. An LTE Rel-8 terminal can receive transmissions on a single component carrier only, provided that the structure of the component carrier follows the Rel-8 specifications. Figure 4 shows an example of the carrier aggregation, where M Rel-8 component carriers are combined together to form MxRel-8 BW, e.g. 5 x 20MHz = 100MHz given M = 5. Rel-8 terminals receive/transmit on one component carrier, whereas LTE-Advanced terminals may receive/transmit on multiple component carriers simultaneously to achieve higher bandwidths.

Moreover, it is required that LTE-A should be backwards compatible with Rel-8 LTE in the sense that a Rel-8 LTE terminal should be operable in the LTE-A system, and that a LTE-A terminal should be operable in a Rel-8 LTE system.

Further with regard to LTE/LTE-A C-plane latency requirements (constraint of response time of RACH procedure), for the LTE C-plane latency requirement the transition time (excluding downlink paging delay and NAS signaling delay) is of less than 100 ms from a camped-state, such as Release 6 Idle Mode, to an active state, such as Release 6 CELL_DCH, in such a way that the user plane is established. The transition time (excluding DRX interval) is less than 50 ms between a dormant state, such as Release 6 CELL_PCH, and an active state, such as Release 6 CELL_DCH. With regard to the LTE C-plane capacity requirement, a large number of users per cell can have quasi-instantaneous access to radio resources in the active state. At least 200 users per cell should be supported in the active state for spectrum allocations up to 5 MHz, and at least 400 users for higher spectrum. A much higher number of users are expected to be supported in the dormant and camped state.

Figure 5 shows the LTE C-plane latency requirement, as per 3GPP TR 25.913 V8.0.0, (2008-12) Technical Report 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN) (Release 8).

Figure 6 reproduces Figure 7.1 of 3GPP TR 36.913 V8.0.1, and shows the LTE-A C-plane latency requirement.

The LTE-A C-plane latency requirement is significantly decreased as compared to LTE Rel-8. The C-Plane latency takes into account RAN and CN latencies (excluding the transfer latency on the SI interface) in unloaded conditions. The transition time from Idle mode (with IP address allocated) to the Connected mode is less than 50 ms, including the establishment of the user plane (excluding the SI transfer delay). The transition time from a "dormant state" in Connected Mode (i.e., DRX substate in Connected Mode in E-UTRAN) is less than 10 ms (excluding the DRX delay). Only 10ms is available for RRC connection wake up. With regard to the LTE-A capacity requirement, there should be support for at least 300 active users without DRX in a 5 MHz bandwidth, while the same number of RRC connections with DRX as in Rel-8 E-UTRA and E-UTRAN (16,000) is expected. However, the control plane latency in LTE-A is even more aggressive than LTE, as in LTE there are 100ms from the RRC_idle state to the RRC_connected state, and 50ms from "out of sync" to "in sync" in RRC_connected state, while in LTE-A there are 50ms from the RRC_idle state to the RRC_connected state, and only 10ms from the "out of sync" to "in sync" in RRC_connected state. Because of the more stringent latency requirement of LTE-A, fewer preamble collisions are allowed and more RACH resources (per UE) are needed than in LTE Rel-8.

In the LTE Rel-8 system there are at least two parameters that are directly related to the RACH load. These are the backoff parameter and the RACH configuration (basically the number of RACH resources per 10 ms). The eNB estimates the RACH load and selects these parameters accordingly and broadcasts them to the UEs.

In general, a radio protocol is very efficient if the signaling procedure is straight forward. However, the RACH procedure represents a major challenge to the C-plane latency of LTE-A due at least to the inherent risk of collision (and subsequent backoff and the iteration of contention between multiple UEs).

SUMMARY

The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.

In a first aspect thereof the exemplary embodiments of this invention provide a method that comprises receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers; selecting a random access channel based at least in part on the received load indications; and transmitting on the selected random access channel. In another aspect thereof the exemplary embodiments of this invention provide an apparatus that comprises a processor and a memory including computer program code. The memory and computer program code are configured to, with the processor, cause the apparatus at least to perform, receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers; selecting a random access channel based at least in part on the received load indications; and transmitting on the selected random access channel. In another aspect thereof the exemplary embodiments of this invention provide a method that comprises determining a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers; transmitting the determined load indications into a cell; and receiving transmissions from a plurality of user equipment on certain random access channels that are selected by individual ones of the user equipment in accordance with the transmitted load indications.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached Drawing Figures:

Figure 1 reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system. Figure 2 shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

Figure 3 illustrates estimated RACH load of Random/Dedicated Signatures, and reproduces Figure 2 of R2-070205.

Figure 4 shows an example of carrier aggregation for the LTE-A system. Figure 5 shows a LTE C- lane latency requirement, and reproduces Figure 6.1 of 3GPP TR 25.913 V8.0.0.

Figures 7 and 8 are each a logic flow diagram illustrating the operation of a method, and a result of execution of computer program instructions embodied on a computer readable medium, in accordance with the exemplary embodiments of this invention.

DETAILED DESCRIPTION

In previous cellular systems, such as HSPA and LTE Rel-8, the terminal has only one carrier present. As such, the issue of RACH load balancing amongst different component carriers does not exist. Any existing carrier load balancing is based on carrier reselection, wherein the terminal selects the RACH/preamble without a priori knowledge of the RACH load per CC.

An aspect of the exemplary embodiments of this invention is to provide flexible RACH load balancing by the use of RACH load indicator bits on a BCH in a multiple CC wireless communication system.

Before describing in further detail the exemplary embodiments of this invention, reference is made to Figure 2 for illustrating a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention that have been described above. In Figure 2 a wireless network 1 is adapted for communication over a wireless link 11 with an apparatus, such as a mobile communication device which may be referred to as a mobile station, which may be a UE 10, via a network access node, such as a Node B (base station), and more specifically an eNB 12. The network 1 may include a network control element (NCE) 14 that may include the MME/SGW functionality shown in Figure 1, and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the internet). The UE 10 includes a controller, such as a computer or a data processor (DP) 10A, a computer-readable memory medium embodied as a memory (MEM) 10B that stores a program of computer instructions (PROG) IOC, and a suitable radio frequency (RF) transceiver 10D for bidirectional wireless communications with the eNB 12 via one or more antennas. The eNB 12 also includes a controller, such as a computer or a data processor (DP) 12A, a computer-readable memory medium embodied as a memory (MEM) 12B that stores a program of computer instructions (PROG) 12C, and a suitable RF transceiver 12D for communication with the UE 10 via one or more antennas. The eNB 12 is assumed to be associated with at least one cell within which a plurality of the UEs 10 can be present at any given time. The eNB 12 is coupled via a data / control path 13 to the NCE 14. The path 13 may be implemented as the SI interface shown in Figure 1. The eNB 12 may also be coupled to another eNB via data / control path 15, which may be implemented as the X2 interface shown in Figure 1.

For the purposes of describing the exemplary embodiments of this invention the UE 10 may be assumed to also include a RACH unit or function 10E, and the eNB 12 also includes a RACH unit or function 12E. The operation of the RACH units/functions 10E, 12E is described in detail below.

At least one of the PROGs IOC and 12C is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 10A of the UE 10 and/or by the DP 12A of the eNB 12, or by hardware, or by a combination of software and hardware (and firmware). The RACH units/functions 10E, 12E may thus also be implemented at least in part by computer software, or by hardware, or by a combination of software and hardware (and firmware).

In general, the various embodiments of the UE 10 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

The computer readable MEMs 10B and 12B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 10A and 12A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architectures, as non-limiting examples.

As was made evident above, the overall functionality of the random access procedures between the UE 10 and the eNB 12 have an important bearing on the ability of the system 10 to conform to LTE-A operational requirements.

A further issue to consider is the unequal RACH performance in non-contiguous CCs. In general, the path-gain of the radio channel and the RACH power control parameters affect the RACH performance, provided that there is the same RACH load traffic model (hot spot, rural cell, cell radius, or proportion of initial access and RRC connection re-establish), back-off scheme, and so forth applies to the non-contiguous CC case. As should be appreciated, a proper and effective RACH load balance scheme is required for RACH performance optimization under various conditions (e.g., different load traffic, different radio conditions).

A further issue to consider is the unequal RACH resources per CC due to different TDD UL/DL slot ratios per CC. For example, a different TDD UL/DL slot ratio per CC is possible when the LTE-A UE 10 has additional RF power amplifiers in the case of non-contiguous carrier aggregation. The RACH resource per CC can be different in this case. In general, the RACH resources and RACH procedures represent a potential impediment in the LTE/LTE-A system. A proper RACH load balancing scheme is needed to deal with at least the following issues:

a) RACH resources are critical as compared to the RACH load in a LTE cell;

b) the stringent LTE-A C-plane latency requirement requires that there be a reduced number of RACH collisions and RACH collision-related procedures, such as collision resolution including backoff;

c) a different RACH processing gain is due to a large path gain difference between non-contiguous CCs, wherein the RACH performance is different between CCs, provided the same RACH load, same number of preamble sequences and same RACH power control parameters exist; and.

d) the presence of unequal RACH resource per CC due to different TDD UL/DL slot ratios per CC.

It is pointed out that a RACH load indicator scheme and a carrier reselection scheme both have the potential to distribute the RACH load over certain carriers. However, the former approach efficiently directs the UE 10 to a desired RACH with the use of a priori information. The carrier reselection approach, however, can require more time to perform, due at least to the needed signaling procedure(s) after the UE 10 discovers that it has selected an improper carrier for RACH use.

It is noted that in LTE-A as finally specified there may be one BCH per CC, although even with one BCH per CC every BCH could carry at least some broadcast information also for the other CCs. For example, every BCH could include information that describes the carrier aggregation configuration (how many carriers there are in total and where they are positioned in frequency), and what the load indicators are for the RACHs on all the carriers. It may also be possible that some DL CCs do not have a BCH, as may be the case in certain asynchronous configurations where there are more DL than UL CCs.

The exemplary embodiments of this invention provide a flexible RACH load balancing procedure in a multi-CC scenario.

In accordance with the exemplary embodiments of this invention, the UE 10 is enabled to access different RACHs on different CCs in, for example, the LTE-A system. The efficient RACH load balancing in the multiple-CC scenario is important to ensure good RACH performance according to different resource conditions. These exemplary embodiments can beneficially be used when there are Rel-8/9/10 UEs 10 coexisting in the LTE-A system, and thus are backwards compatible with UE releases that predate LTE-A .

The exemplary embodiments of this invention make use of RACH load indicator bits that are signaled (broadcast) into the cell by the eNB 12. These RACH load indicator bits instruct and/or aid the UE 10 in selecting RACHs in different CCs flexibly according to the system RACH load situation and RACH access policies per CC. In the exemplary embodiments the BCH carries information to enable the eNB 12 to influence the RACH load distribution on different CCs. The UE 10 thus is enabled to select more intelligently between RACHs on different CCs by using the BCH information.

The operation of the exemplary embodiments may be as follows. 1.) The eNB 12 measures the RACH load per CC, and determines a set of "RACH load indicator bits" according to a carrier access policy.

la.) The RACH load may include random access requests from Rel-8/9/10 UEs, and thus the technique is adaptive to and supports Rel-8/9/10 UE 10 coexistence, lb.) A Rel-10 eNB 12 can distinguish the RACH load from Rel-8/9/10 UEs, and may derive different RACH load indicator bits according to different policies as described in further detail below.

2.) The eNB 12 broadcasts information, which may be referred to for convenience as "RACH load indicator bits per CC", in the LTE-A cell, thereby informing the UEs 10 within the cell of the opportunities to access RACHs on different CCs.

3.) The Rel-10 (LTE-A) UE 10 accesses the RACH on the desired CC according to the received RACH load indicator bits information.

This approach is clearly different than simple UE 10 carrier selection. If for some reason one or more carries are blocked, the RACH load cannot be distributed over the blocked carrier(s) and some RACH resources are wasted. The use of the flexible RACH load balance per CC approach in accordance with the exemplary embodiments of this invention decreases the collision probability and generally improves the overall RACH performance.

The RACH load indicator bits per CC may be derived by the RACH function 12E of the eNB 12 in different scenarios by use of the following exemplary policies.

A. ) Equal RACH load balance per CC: In this case a Rel-10 (LTE-A compatible) UE 10 selects a proper RACH on a certain CC to ensure equal load balancing. In some cases Rel-8/9/10 UEs 10 may initiate RACH procedure on the same set of CCs. However, the RACH load on certain CCs can become unbalanced due to Rel-8/9 UEs that are camping. The RACH load of the LTE-A UEs 10 is preferably balanced to ensure good RACH performance. Equal RACH load balance of a purely LTE-A UE 10 can be achieved by this technique as well.

B. ) Non-contiguous CC or different radio channel conditions: In this case the RACH demodulation performance can be very different due to different path gains in different CCs. In this case the RACH load indicator bits are adaptive to each CC.

C. ) Heterogeneous deployment, different priority of autonomous carrier selection in SON, relay cells and home eNB cells: In this case different CC/cells may have a different access priority class. A flexible scheme is needed to accommodate this situation. For example, radio channel conditions, the UE 10 power class and the power control parameters of the RACH impact the RACH optimization in a SON. D. ) Different UL/DL slot ratios per CC in TDD carrier aggregation: In this case the eNB 12 determines or derives/composes the RACH load indicator bits per CC to accommodate different RACH resources on different CCs with different UL/DL slot ratios.

E. ) Capacity optimization/QoS differentiation in (non-) contiguous CCs: For example, flexibility of load balancing per CC is desired by the eNB 12 according to capacity optimization/QoS differentiation. The QoS of an emergency call, high vehicle speed call, or a poor path-gain call can be met in lightly loaded CC.

It can be noted that carrier selection in the RRC_idle state in LTE/LTE-A is possible with the use of these exemplary embodiments.

Several non-limiting examples are now provided as to how the RACH load indicator bits may be derived/composed by the eNB RACH function 12E.

Example 1:

The RACH load indicator bits are provided as limited ranks, such as "unhappy", "ok", "happy", etc., where "happy" indicates a light RACH load on a particular CC, while "unhappy" indicates a heavy load on the CC.

Example 2:

The RACH load indicator bits are provided as a relative selection probability P_; for the i-th carrier. In this case the RACH function 10E of the UE 10 selects the i-th

/ M

y _i P_i , where M is the total number of CCs. P_; s may i=l

be quantized with, for example, 2-3 bits in order to provide sufficient flexibility for load balancing. However, only one bit per RACH may also be used. If it is specified that P_; can have only values 0 and 1, load indications can forbid completely selection of certain CCs while the remainder of the CCs can be accessed with equal probability. RACH on a forbidden CC could then be reserved for Rel-8 UEs and for non-contention access. Example 3:

If a one-to-one correspondence between BCH and RACH is defined, the UE 10 needs to decode all the BCHs before it can select RACH. An alternative implementation is that each BCH contains carrier aggregation information including load indicators for all RACHs. Both signaling schemes can be applied in symmetric carrier aggregations where each DL CC contains a BCH and corresponds to one UL CC. Both schemes are applicable also with those asymmetric carrier aggregations where there are more DL than UL CCs. However, in asymmetric configurations with more UL than DL CCs a BCH may be common for two or more UL CCs and may necessarily carry load indicators for more than one RACH.

The use of the exemplary embodiments of this invention provides a number of advantages and technical effects.

For example, the use of these exemplary embodiments provides improved efficiency, as the use of the RACH load indicator bits is more efficient than the use of the conventional, legacy carrier reselection scheme in informing the RACH decision making functionality 10E of the UE 10. In general, carrier reselection requires a more involved signaling procedure once the UE 10 discovers that it has selected an improper carrier.

Further by example, the use of these exemplary embodiments is compatible with existing RACH procedures, as they are operable with current (fast) control parameters (back-off time, etc.), schemes of the Rel-8 RACH. The flexible RACH load balance approach may be considered as typically a slow procedure. For example, the update interval may be some multiple of the typical BCH information update interval, such as 80ms in Rel-8. Further by example, the use of these exemplary embodiments is adaptive to Rel-8/9/10 UE 10 coexistence, as this flexible RACH load balance approach is transparent to Rel-8/9 UEs, while the Rel-10 (LTE-A) UE 10 RACH selection scheme efficiently selects the proper RACH on a certain CC according to the Rel-8/Rel-9 UE 10 RACH load per CC, as well as other policies of interest.

Further by example, the use of these exemplary embodiments provides a RACH load balancing scheme in the multi-CC scenario in the LTE/LTE-A system. The eNB 12 is enabled to control, or at least influence, the UE 10 RACH selection, thereby giving the eNB 12 flexibility for achieving a desired load balancing, e.g., whether to establish a balanced RACH load or an imbalanced RACH load across CCs. Further by example, the use of these exemplary embodiments provides advantages over conventional techniques of selecting the channels at the network side since, specifically for random access channels, this requires the UEs to be constantly reconfigured in accordance with the load, as the load continuously shifts as a result of at least DTX behavior. The basic nature of RACH operation is such that the timing of RACH transmissions are unpredictable (i.e., random).

As a simple and non-limiting example, if a CC would be defined as one of the Carriers 1, 2, etc. shown in Figure 4, in one case the RACH indicator bits may be a 5-bit field, where the state of each bit would indicate the suitability/non-suitability of the associated CC, assuming at least that every BCH (on different CCs) would contain information on the entire aggregation configuration.

Figure 7 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 7A, a step of receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers. At Block 7B there is a step of selecting a random access channel based at least in part on the received load indications. At Block 7C there is a step of transmitting on the selected random access channel. In accordance with the method of the preceding paragraph and Figure 7, the load indications comprise a set of bits each having one of two states for indicating a current load of an associated component carrier. In accordance with the method of Figure 7, the load indications each indicate a relative selection probability of an associated component carrier.

In accordance with the method of Figure 7, where the load indication for each of the plurality of component carriers is received from a downlink broadcast channel.

In accordance with the method of the preceding paragraph, where there is a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, or where there not a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, and further comprising receiving additional information to indicate which uplink carriers the received load indications refer to.

In accordance with the method of Figure 7, where one broadcast channel contains load indications for random access channels on a plurality of component carriers.

In accordance with the method of Figure 7, where the load indication for each of the plurality of component carriers is received from a downlink broadcast channel, and where the received load indications are updated at a multiple of an information update period of the downlink broadcast channel.

In accordance with the method of the preceding paragraphs and Figure 7, where the received load indications are indicative of a network access node desired loading of individual ones of the component carriers. In accordance with the method as in any one of preceding paragraphs and Figure 7, where the method is performed as a result of the execution of computer program code by a data processor, where the computer program code is stored in a memory, and where the data processor and the memory comprise part of a user equipment.

Figure 8 is a logic flow diagram that illustrates the operation of a further method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 8 A, a step of determining a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers. At Block 8B there is a step of transmitting the determined load indications into a cell. At Block 8C there is a step of receiving transmissions from a plurality of user equipment on certain random access channels that are selected by individual ones of the user equipment in accordance with the transmitted load indications. In accordance with the method of the preceding paragraph and Figure 8, the load indications comprise a set of bits each having one of two states for indicating a current load of an associated component carrier.

In accordance with the method of Figure 8, the load indications each indicate a relative selection probability of an associated component carrier.

In accordance with the method of Figure 8, the load indication for each of the plurality of component carriers are transmitted on a downlink broadcast channel, where in one case there is a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, and in another case there not a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, and further comprising transmitting additional information to indicate which uplink carriers the transmitted load indications refer to. In accordance with the method of the preceding paragraph, further comprising updating and transmitting the load indications at a multiple of an information update period of the downlink broadcast channel. In accordance with the method of the preceding paragraphs, where the load indications are determined based on a network access node desired loading of individual ones of the component carriers, where the component carriers are one of contiguous component carriers or non-contiguous component carriers.

In accordance with the method of the preceding paragraph, where the load indications are determined to accommodate different random access channel resources on different component carriers having different uplink/downlink slot ratios.

In accordance with the method of the preceding paragraph, performed as a result of the execution of computer program code by a data processor, where the computer program code is stored in a memory, where the data processor and the memory comprise part of the network access node, such as an eNodeB.

The blocks shown in Figures 7 and 8 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). The exemplary embodiments of this invention further provide an apparatus comprising means for receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers; means for selecting a random access channel based at least in part on the received load indications; and means for transmitting on the selected random access channel.

The exemplary embodiments of this invention further provide an apparatus comprising means for determining a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers; means for transmitting the determined load indications into a cell; and means for receiving transmissions from a plurality of user equipment on certain random access channels that are selected by individual ones of the user equipment in accordance with the transmitted load indications.

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention. For example, while the exemplary embodiments have been described above in the context of the E-UTRAN (UTRAN-LTE) and LTE-A systems, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only these particular types of wireless communication system, and that they may be used to advantage in other wireless communication systems that employ multiple carriers and a random access procedure.

It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples. Further, the various names used for the described parameters (e.g. "RACH load indicator bits", etc.) are not intended to be limiting in any respect, as these parameters may be identified by any suitable names. Further, the various names assigned to different channels (e.g., BCH, RACH, etc.) are not intended to be limiting in any respect, as these various channels may be identified by any suitable names.

Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMS What is claimed is:

1. A method, comprising:

receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers;

selecting a random access channel based at least in part on the received load indications; and

transmitting on the selected random access channel.

2. The method of claim 1, where the load indications comprise a set of bits each having one of two states for indicating a current load of an associated component carrier.

3. The method of claim 1, where the load indications each indicate a relative selection probability of an associated component carrier.

4. The method of claim 1, where the load indication for each of the plurality of component carriers is received from a downlink broadcast channel.

5. The method of claim 4, where there is a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers.

6. The method of claim 1, where one broadcast channel contains load indications for random access channels on a plurality of component carriers.

7. The method of claim 4, where the received load indications are updated at a multiple of an information update period of the downlink broadcast channel.

8. The method as in any one of the preceding claims, where the received load indications are indicative of a network access node desired loading of individual ones of the component carriers.

9. The method as in any one of claims 1 through 7, performed as a result of the execution of computer program code by a data processor, where the computer program code is stored in a memory, where the data processor and the memory comprise part of a user equipment.

10. An apparatus, comprising: a processor; and a memory including computer program code, where the memory and computer program code are configured to, with the processor, cause the apparatus at least to perform, receiving a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers;

transmitting on the selected random access channel.

11. The apparatus of claim 10, where the load indications comprise a set of bits each having one of two states for indicating a current load of an associated component carrier.

12. The apparatus of claim 10, where the load indications each indicate a relative selection probability of an associated component carrier.

13. The apparatus of claim 10, where the load indication for each of the plurality of component carriers is received from a downlink broadcast channel.

14. The apparatus of claim 13, where there is a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers.

15. The apparatus of claim 10, where one broadcast channel contains load indications for random access channels on a plurality of component carriers.

16. The apparatus of claim 13, where the received load indications are updated at a multiple of an information update period of the downlink broadcast channel.

17. The apparatus as in any one of the preceding claims 10 through 16, where the received load indications are indicative of a network access node desired loading of individual ones of the component carriers.

18. The apparatus as in any one of claims 10 through 16, where the processor and the memory comprise part of a user equipment.

19. A method, comprising: determining a load indication for each of a plurality of component carriers, where an individual one of a plurality of random access channels are associated with an individual one of said plurality of component carriers;

transmitting the determined load indications into a cell; and

receiving transmissions from a plurality of user equipment on certain random access channels that are selected by individual ones of the user equipment in accordance with the transmitted load indications.

20. The method of claim 19, where the load indications comprise a set of bits each having one of two states for indicating a current load of an associated component carrier.

21. The method of claim 19, where the load indications each indicate a relative selection probability of an associated component carrier.

22. The method of claim 19, where the load indication for each of the plurality of component carriers are transmitted on a downlink broadcast channel, where in one case there is a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, and in another case there not a one-to-one correspondence between downlink broadcast channels and uplink random access channel carriers, and further comprising transmitting additional information to indicate which uplink carriers the transmitted load indications refer to.

23. The method of claim 22, further comprising updating and transmitting the load indications at a multiple of an information update period of the downlink broadcast channel.

24. The method as in any one of the preceding claims 19 through 23, where the load indications are determined based on a network access node desired loading of individual ones of the component carriers, where the component carriers are one of contiguous component carriers or non-contiguous component carriers.

25. The method as in claims 24, where the load indications are determined to accommodate different random access channel resources on different component carriers having different uplink/downlink slot ratios.

26. The method as in claim 25, performed as a result of the execution of computer program code by a data processor, where the computer program code is stored in a memory, where the data processor and the memory comprise part of the network access node.

27. A computer program product comprising a program code stored in a computer readable medium configured to perform the method according to any of claims 1 through 9 and 19 through 26.