USER DESCRIPTION     72/1553-HSC 103 12/4 Uen B    

User Description, MAIO Management

Copyright

© Ericsson AB 2003. All rights reserved. No part of this document may be reproduced in any form without the written permission of the copyright holder.

Disclaimer

The contents of this document are subject to revision without notice due to continued progress in methodology, design and manufacturing.

Ericsson shall have no liability for any error or damages of any kind resulting from the use of this document.

Contents

1 Introduction

2 Glossary 2.1 Concepts 2.2 Abbreviations and Acronyms

3 Capabilities

4 Technical Description 4.1 General 4.2 Algorithm 4.3 GPRS/EGPRS 4.4 Main changes in Ericsson GSM system R10/BSS R10

5 Engineering Guidelines 5.1 General 5.2 Application areas and MAIO planning recommendations

6 Parameters 6.1 Main controlling parameters 6.2 Additional parameters 6.3 Value ranges and default values

7 References

1   Introduction

The MAIO Management feature provides increased control over synthesizer frequency hopping to minimize channel interference within a site and synchronized cluster of cells.

2   Glossary

2.1   Concepts

Basic Physical Channel

A Basic Physical Channel (BPC) is a physical channel on one timeslot in the TDMA frame in the radio interface between the BTS and the MS. With the feature Frequency Hopping (FH) the frequency will change between TDMA frames for each connection. Without FH a single frequency is used. See Figure 1.

 Hopping Group A hopping group (HG) is a group of BPCs in the same cell, using

the same timeslot number in the TDMA frame but on different transceiver, configured so that they are all hopping using the same set of frequencies. See Figure 1 .

 Channel Group A CHannel GRoup (CHGR) is a group of frequencies. There can be

more than one CHGR defined in a cell. A frequency may be defined in more than one CHGR per cell (except for the BCCH carrier). CHGRs are operator controlled and facilitate control over groups of frequencies in a cell. CHGRs are identified by a local channel group number defined per cell. CHGR 0 contains the BCCH and is defined automatically at cell definition. See Figure 1.

 Hopping Frequency Set

A Hopping Frequency Set (HFS) specifies a group of frequencies which a CHGR may use to hop over. To benefit from MAIO Management, HFSs within a site or synchronized cells must have equal number of frequencies.

 Hopping Sequence Number

The Hopping Sequence Number (HSN) specifies in which order the frequencies in the HFS shall be used for a CHGR when using frequency hopping. The sequence to be used can be either be a cyclic sequence or various pseudo-random sequences. To benefit from MAIO Management, cells within a site must have the same HSN.

 Synchronized cells

Synchronized cells referes to cells that are possible to have their timing functions adjusted to perfectly align the TDMA frames in time. The cells may belong to a site, or belong to different sites. Synchronized cells, configured with the same HSN, have the possibility to have their TDMA frame sequences starting at the same instant in time.

 Mobile Allocation Index Offset

Mobile Allocation Index Offset (MAIO) is a frequency offset set for all Basic Physical Channels (BPCs). Manual MAIO planning prevents co- and adjacent channel interference within a cell as well as in co-sited or synchronized cells when using frequency hopping (see User Description, Frequency Hopping).

 Transceiver Group

A Transceiver Group (TG) represents a group of managed objects (e.g. transmitter, receiver) belonging to the same BTS.

 

Figure 1   Definition of BPCs, HGs & CHGRs for a cell

2.2   Abbreviations and Acronyms

BPC Basic Physical Channel CHGR

Channel Group

 FN Frame Number HFS Hopping Frequency Set HO Handover HSN Hopping Sequence Number MAIO Mobile Allocation Index Offset TG Transceiver group TS Timeslot 

3   Capabilities

MAIO Management provides increased control over synthesizer frequency hopping to avoid co- and adjacent channel interference within a cell as well as in co-sited or synchronized cells. This is beneficial in a network with tight re-use of frequencies such as 1/1 & 1/3.

Note that MAIO Management only increases control over the interference between cells if the cells are synchronized, i.e. cells within a site using one TG or a site using Transceiver Group Synchronization or Synchronized Radio Networks (see User Description, Transceiver Group Synchronisation and User Description, Synchronized Radio Networks).

MAIO Management introduces the possibility to allocate a MAIO list manually for each CHGR. The feature allows the operator to control which MAIO values are to be allocated to the HGs within a CHGR. This can be achieved by either explicitly defining a MAIO list manually or by specifying that the default order is to be used.

4   Technical Description

4.1   General

Mobile Allocation Index Offset (MAIO) is a frequency offset set for all Basic Physical Channels (BPCs). The MAIO Management feature gives the capability to define MAIO lists manually. Manual MAIO planning prevents adjacent channel interference within a cell as well as co- and adjacent channel interference in co-sited cells when using synthesizer frequency hopping, see User Description, Frequency Hopping. If a frequency is used in more than one CHGR in a cell, usage of MAIO Management is a prerequisite to prevent co-channel interference within the cell.

At tight frequency re-use such as 1/1 (which means that the HFSs are identical for all cells), the cells on a site (if there are more than one cell on the site) can be prevented from sending on the same frequency at the same time by using different values in the cells' MAIO lists. This, however, requires that all transceivers within the site are synchronized, the HFSs contain equal number of frequencies and the same HSN are used for the CHGRs. Synchronization can be achieved if all transceivers belong to the same Transceiver Group (TG) or if the TGs are synchronized (User Description, Transceiver Group Synchronisation & User Description, Synchronized Radio Networks).

4.2   Algorithm

At frequency hopping MAIO values are used (together with the HSN and the current FN) to point out the frequencies to be used from the HFS at an instant in time. The formula used to do this is (simplified here with cyclic hopping and depicted in Figure 2 ):

"pointer" = (MAIO+FN) modulo(number of frequencies in HFS)

For pseudo random hopping, FN is replaced with a pseudo random hopping value (which is based on FN):

"pointer" = (MAIO+random value) modulo(number of frequencies in HFS)

This means that the order in which the BPCs frequencies are changing between each TDMA frame is decided by the HSN but with an offset decided by the MAIO values.

Figure 2   The MAIO values are used to point out which frequencies to be used at an instant in time. The current FN is 1. For MAIO=0 the "pointer" will be 1 and point at

the second position in the HFS (freq 4). (To point at the first position the "pointer" has to be 0.) In the next TDMA frame (FN 2) the pointers will be shifted downwards one

step for cyclic hopping. For MAIO=0 the "pointer" will then be 2 and point at the third position in the HFS (freq 7).

When a CHGR is defined it will either use the default MAIO list or the MAIO list defined by the operator. A MAIO list contains MAIO values (e.g. 2, 5, 8) and are automatically assigned to the BPCs within each HG at the initial configuration of CHGRs. No MAIO values are allowed to be identical within a MAIO list.

Default MAIO list:

The number of MAIO values in the default list is the same as the number of frequencies in the HFS. The values themselves stretch from 0 up to one less than the number of frequencies in the HFS. E.g. If there are 15 frequencies in the HFS, the MAIO list will contain the values 0-14.

The order of the MAIO values in the default list is arranged in a "first even then odd MAIO values" manner. This means that the beginning of the list will consist of all even MAIO values in ascending order. After these even values all the odd values are arranged in ascending order. E.g. for a HG with HFS containing 7 frequencies the default list will be 0, 2, 4, 6, 1, 3, 5.

The actual MAIO values to be used for a CHGR depend on the number of TRXs for the CHGR. If e.g. three TRXs are used for a CHGR, only the first three MAIO values in the MAIO list will be used. With 7 frequencies in the HFS (as in the previous example), the used default MAIO values would be 0, 2, 4. The remaining values, i.e. 6, 1, 3, 5, will not be used unless additional TRXs are added (see 5.2.).

Manual MAIO list:

A manual MAIO list for a CHGR can be created by specifying up to sixteen values for the parameter MAIO.

If the manual MAIO list is too short (i.e. the length of the MAIO list is less than the number of TRXs for the CHGR), then random MAIO values will be added on to the end of the list. This process will be randomized as much as is reasonable whilst minimizing the risk of having consecutive MAIOs in the list. This means that at installation of an additional TRX for a cell, additional MAIO values will be allocated.

If there is an invalid MAIO value (a value that is equal to or higher than the number of frequencies in the HFS) in the manual MAIO list it will be skipped in favor of the next MAIO value in the list. This means that any invalid MAIO values that are specified by the operator are not allocated and a randomized valid MAIO value will be allocated to the last BPC in the HG.

4.3   GPRS/EGPRS

MAIO Management can be used on GPRS/EGPRS channels in the same way as for circuit switched channels. No measures, or concerns have to be taken.

4.4   Main changes in Ericsson GSM system R10/BSS R10

Up to 128 frequencies can be assigned to a cell. However the limit of frequencies in a CHGR is 32. A frequency can be repeated in several CHGRs within a cell.

5   Engineering Guidelines

5.1   General

When tight re-use of frequencies such as 1/3 and 1/1 is applied on a network, a good MAIO planning strategy will be useful. On neighbour cells the same frequencies and MAIO values (e.g. the default list) can be used as long as the cells are unsynchronized. However, MAIO Management can give more control over the interference in networks with very tight frequency re-use, e.g. 1/1, if MAIO lists are defined manually. MAIO Management requires synthesizer frequency hopping and, for best possible 1/1 planning, groups of synchronized cells in the network (e.g. within a site).

Between sites there will be interference sometimes over time, when the hopping sequences indicate that cells on neighbouring sites shall send on the same frequency at the same instant in time. This is however a minor problem since the GSM standard handles loss of some data.

5.2   Application areas and MAIO planning recommendations

5.2.1   1/1 re-use

When using 1/1 planning in a network all cells within a site (or synchronized cluster) will use identical HFSs. Manual MAIO planning will here help to avoid adjacent channel interference within a cell as well as co- and adjacent channel interference in synchronized co-sited cells. Also co-channel interference within a cell can be avoided

if frequencies are repeated in several CHGRs (see Section 5.2.4). This is done by defining different MAIO lists for each cell (if there is only one hopping CHGR per cell) and for each CHGRs within a cell using the same frequencies. A MAIO value should not be re-used within a site if also the HSN and FNOFFSET values are the same for these CHGRs. Care should be taken when using manual MAIO planning and 1/1 re-use. If an invalid MAIO value or a too short manual MAIO list is allocated to a cell, then a randomized MAIO value will be generated. When this new MAIO value is generated no consideration is taken to the other cells within the site. If a MAIO value is re-used within a site with synchronized cells and 1/1 re-use, bad quality will be achieved.

To synchronize co-sited cells, the CHGRs for all cells can belong to either the same TG or if co-sited TGs are synchronized (User Description, Transceiver Group Synchronisation), several TGs. Check the hardware for the exact capabilities and limitations for different RBSs.

The way of defining MAIO values depends on if there are adjacent frequencies in the HFS or not.

If there are adjacent frequencies within the HFSs, only even (or odd) MAIO values should be used within the site (see example below). Every third of these even (or odd) values should be assigned to each cell within a three sector site. This can be done properly if the number of frequencies in the HFS is equal or greater than two times the number of TRXs in the TG (or synchronized TGs). If this is not the case, even and odd MAIO values have to be used. This will cause adjacent channel interference sometimes over time, but this is a minor problem since the GSM standard handles loss of some data.

For HFSs with no adjacent frequencies, MAIO values can be assigned to each MAIO list in any way as long as the MAIO values are not re-used within a site.

Example:

Assume that in a three sector site (see Figure 3) 12 hopping frequencies are used for CHGR 1 (the hopping CHGR) in each cell. The HFSs are identical for these three hopping CHGRs. The same HSN is used in all cells on the site (in this example HSN 0, cyclic). By having different MAIO values for the 3 cells on the site, interference within and between the cells is minimized.

Figure 3   An example of a site with 6 hopping (HSN=0) & 3 non-hopping TRXs with 12 frequencies in the cells identical HFSs. The current FN is 1. The algorithm (MAIO+FN)modulo 12 is used for allocation of frequencies in the HFS since there are 12 frequencies in the HFSs. Next TDMA frame (FN 2) causes a downward shift, one step, for the arrows. (To allocate the first frequency in the HFS, the result of the algorithm has to be 0.)

5.2.2   1/3 re-use

In a network using 1/3 frequency re-use, all frequencies are re-used in every site (if the site has three sectors). However, the frequencies are split up into three groups, one for each cell. In a 1/3 planned site without Synchronization, only considerations concerning adjacent frequencies within a cell has to be taken. The default value for the parameter MAIO is recommended to be used for each cell since it prevents adjacent channel interference within a cell if there are enough frequencies in the HFS. In this case enough means:

"number of frequencies in the HFS" >= 2*(number of TRXs in the CHGR)

Non-Synchronized cells may however suffer from adjacent channel interference from time to time from within the site. By synchronizing the site, this interference can be avoided as long as the HFSs within the site have the same number of frequencies.

By using a set of consecutive adjacent frequencies in each cell, in combination with MAIO = DEFAULT, adjacent channel interference within a synchronized site will be avoided as shown in Table 1 . See also Figure 4 .

Table 1    By using the default MAIO allocation strategy for a Synchronized site with an adjacent consecutive set of frequencies in each cell, adjacent channel interference can be avoided. The MAIO lists will be (0, 2). The marked frequencies in the table are the ones that are used at an instant in time. For cyclic hopping, the next frequencies used would be: 2, 4, 7, 9, 12, 14.

HFS for cell A HFS for cell B HFS for cell C

> 1 < > 6 < > 11 <

2 7 12

> 3 < > 8 < > 13 <

4 9 14

5 10 15

If all frequencies are spread out evenly between the co-sited cells' HFSs as shown in the table below, at least one manual MAIO list has to be created. E.g. a site configured as Table 2 may have default MAIO lists (i.e. 0, 2) in cell A and cell C. A manual MAIO list has to be created for cell B to minimize the interference (if the site is synchronized). This MAIO list may use the MAIO values that are not yet taken by the default lists, e.g. 1 & 3. At an instant in time the marked frequencies in the table below will be used and interference is in this way avoided. This is further shown in Figure 4 .

Table 2    Adjacent channel interference can here be avoided by using a mixture of two default MAIO lists and a manual MAIO list. The MAIO lists will be (0, 2) for cell A and cell C. Cell B requires the manual MAIO list: (1, 3). The marked frequencies in the table are the ones that are used at an instant in time. For cyclic hopping, the next frequencies used would be: 4, 6, 8, 10, 12, 14.

HFS for cell A HFS for cell B HFS for cell C

> 1 < 2 > 3 <

4 > 5 < 6

> 7 < 8 > 9 <

10 > 11 < 12

13 14 15

Figure 4   Comparison between a configuration with adjacent frequencies in the HFSs (left site - "Blocked") and a configuration with evenly spread out frequencies in the HFSs (right site - "Staggered"). The "adjacent" (or "Blocked") configuration can use the default list in each cell. The "evenly spread out" (or "Staggered") configuration

can also use the default list (i.e. 0, 2) except for the, in figure, lower right cell. In this cell a manual MAIO list has to be defined (i.e. 1, 3) to minimize interference.

5.2.3   Adding a TRX in the CHGR

When adding a TRX for a cell, an extra MAIO value has to be added to this CHGR. If no extra MAIO value is manually assigned to the MAIO list, the feature will assign an extra MAIO value randomly.

In the example for 1/1 in Figure 3 , adding a TRX for cell A would call for e.g. 3, 9 or 11 as an extra MAIO value. If MAIO value 11 is chosen the MAIO list would in this case be 0, 6, 11 for cell A. This will cause some adjacent channel interference within cell A since the HFS has some adjacent frequencies included. To avoid this problem, MAIO value 3 or 9 should be added instead of 11. If many or all frequencies in the HFS are adjacent, then adding an extra frequency to the HFSs has to be considered.

If the new TRX does not belong to the same TG as the other TRXs, reuse of the frequencies within a cell should be considered. See Section 5.2.4.

5.2.4   Reuse of frequencies within a cell

It is permitted to reuse the same frequency in CHGRs within a cell. When expanding a cell with TRXs from a different TG, these new TRXs can not exist in the same CHGR. By defining the HFS of the new CHGR exactly the same as the earlier defined CHGR (presuming only one hopping CHGR previously) all hopping frequencies will be used for all connections. (This is preferred compared to splitting the earlier HFS and use half of the frequencies in each of the two CHGRs.)

It is important that the same frequency is not used at the same time in both the CHGRs. By having different MAIO values for each CHGR, e.g. odd values in one and even in the other, collisions are avoided.

Note that it is important that the HFSs are exactly the same. (Synchronization will be destroyed with one frequency left out.)

5.2.5   Synchronized Radio Networks

When synchronization is done between cells of more than one site, i.e. synchronizing partly or all of the network, MAIO management can be used to decrease the co- and adjacent channel interference even further. For further information on synchronizing the network, see User Description, Transceiver Group Synchronisation and User Description, Synchronized Radio Networks. The general approach of the Ericsson methodology is to view all cells within a synchronized cluster in the same way as a normal site but with more than three sectors.

However there are some standard related technical issues to consider to gain the most of such planning. If the difference of FNOFFSET is 0 or 51, e.g. FNOFFSET is the same in all cells, there is a big risk of prolonged duration time of the measurement procedure of neighbour cells due to the length of the multiframe. Therefore FNOFFSET planning also has to be performed to avoid this. (E.g. Do no use FNOFFSET = 8 everywhere or combine the value 0 with 51 in all cells in the network.) The measurement duration may not be harmful if there are just a few neighbours, e.g. an indoor system or a very well planned outdoor system with few neighbours.

The size of a synchronized cluster of sites is a case by case issue depending on number of neighbour relations and interference situations.

Example:

A 1/3 network is network synchronized from being only synchronized within a site. The operator has got 20 frequencies to use for frequency hopping on three TRXs per sector. However only 18 have been used due to the previous site-only synchronized network planning limitations, i.e. same number of frequencies in the HFSs' of the synchronized cells. The three HFSs have each a block of six adjacent frequencies. The frequency plan will be kept in the new configuration.

In the new configuration the same MAIO plan of the default MAIO list (i.e. 0,2,4) is used in half the cells while odd MAIO values (i.e. 1,3,5) are used in the rest of the cells according to Figure 5. The reason for this is to control the interference between the now synchronized neighbouring sites. As can be seen Cell A in both sites with identical HFS will get rid of all co-channel interference.

Another difference compared to the previous configuration is the introduction of FNOFFSET planning. The reason for this is to avoid the longer measurement procedure that will take place when having the same FNOFFSET or multiples of 51. Using different offsets will however not affect the benefit of network synchronization as long as FNOFFSET is the same for groups of cells with the same HSN. As can be seen there is a distance between the FNOFFSET values used (in this case 5). The reason for this is that if for some reason the synchronization stops working, then time drifts do not immediatly allign the TDMA offset.

One last thing that can be applied is to include the two last frequencies that were left over in the previous cell plan. As the sectors are not longer frequency synchronized

these extra frequencies in one of the cells HFS will give opportunity for an extra TRU or to lower the interference even more.

Figure 5   Solution of a 1/3 reuse synchronized network. The configuration for the two described sites is repeated throughout the synchronised cluster/network.

If the operator in this case had even more frequencies, e.g. twice as many in each sector, then preferrably another MAIO plan shall be applied to avoid adjacent channel interference between sites. This can be done by using e.g. only even MAIO values, in this case MAIO = 0,2,4 and MAIO = 6,8,10 (see Figure 6). If even more frequencies are available, then having a third site with MAIO = 12, 14, 16 should be considered.

Figure 6   With many frequencies MAIO Management can be used to avoid all adjacent channel interference between Synchronized sites in a 1/3 reuse network.

5.2.6   Hopping with BCCH frequency carrier included

When the BCCH frequency carrier is included in the hopping CHGR, the HG on timeslot number 0 will have one MAIO value less than the other HGs. This is due to that TS 0 on the BCCH carrier frequency does not hop.

5.2.7   Baseband hopping

There is no benefit in manual MAIO planning for baseband hopping. The reason is that all TRXs in a CHGR are available for traffic at the same time. Interference within and between cells can therefore not be avoided with MAIO Management. Interference between cells can be battled by using other Ericsson features such as Intra-Cell Handover and Idle Channel Measurements (see User Description, Intra Cell Handover and User Description, Idle Channel Measurements).

6   Parameters

6.1   Main controlling parameters

MAIO is a parameter that will allow the operator to specify a list of up to 16 MAIOs, in the order in which they are to be allocated to a channel group. This parameter can also be set to DEFAULT, which removes the manual MAIO list in favor for the default MAIO list. This parameter is set per CHGR.

6.2   Additional parameters

HOP is the switch for turning frequency hopping on or off, defined per channel group. HOP = ON defines that all channels except the BCCH hop. HOP = OFF defines that the hopping status for the channel group is non-hopping.

HSN is the hopping sequence number, defined per CHGR. This parameter specifies which hopping sequence to be used. All timeslots in one channel group are configured with the same HSN. HSN = 0 yields a cyclic sequence. HSN = 1 to 63 yields pseudo-random sequences. Due to the procedure used by the mobile stations for measurement reporting, the use of cyclic hopping with a multiple of 13 frequencies should be avoided especially when DTX is used , see User Description, Discontinuous Transmission. (For measurement reporting when using DTX, a subset of TDMA frames, SACCH, are used for the measurements which is sent every 13:th TDMA frame. Cyclic hopping on 13 frequencies will in this case only consider one of the frequencies.)

FHOP selects which hopping method to be used, baseband (FHOP = BB) or synthesizer (FHOP = SY) hopping. It is defined per TG.

FNOFFSET indicates the time difference from the FN generator in the BTS. If Synchronization is to be achieved within a site FNOFFSET should be the same for all cells within the site unless network synchronization is used, see User Description, Transceiver Group Synchronisation and User Description, Synchronized Radio Networks.

COMB specifies which combiner type that has been connected, a wide-band hybrid combiner (COMB = HYB) or a narrow-band filter combiner (COMB = FLT). It is defined per TG. If a filter combiner is connected, only baseband hopping can be used.

6.3   Value ranges and default values

Table 3   

Parameter name Default value Recommended value

Value range Unit

MAIO DEFAULT - 0 to 31 or DEFAULT

-

HOP OFF ON OFF, TCH, ON -

HSN - Use the same HSN for synchronized co-sited cells. Avoid using HSN

= 0.

0 to 63 -

FHOP - SY BB, SY -

FNOFFSET 0 Dependent on size of synchronized cluster

0-1325 -

COMB - HYB HYB, FLT -

7   References

1. User Description, Transceiver Group Synchronisation 2. User Description, Frequency Hopping 3. User Description, Discontinuous Transmission 4. User Description, Intra Cell Handover 5. User Description, Idle Channel Measurements 6. User Description, Synchronized Radio Networks