Doc. SE19(12)XX

59th meeting of PT SE 19

ECO, Copenhagen, Denmark, 12-13 June 2012

Date issued: 7-June-2012

Source: SIAE Microelettronica SpA

Subject: Impact of asymmetric deployment on channel arrangement and equipment HW (28 / 14 MHz go/return example)

Summary

This contribution responds to an action item taken during the first Conf-Call and not yet fulfilled.

We still remain much dubious about the effective spectrum efficiency improvement of asymmetric deployment.

Nevertheless, the document analyses the possible coupling (go/return) of different size channels in bands were channel arrangements of various size are presently provided paired in conventional mode with constant duplex separation.

Asymmetry automatically implies variable duplex separation; the variability amount is function of the assumed go/return coupling within the channel arrangement.

We believe that a complete freedom of choice of go/return channel would not be practical from the equipment HW (duplex filters) implementation point of view. Definite rule of go/return coupling should be defined for reducing (or at least for clearly define) the duplex variability.

Three examples, in line with possible different approaches and common use practice when different (symmetric) channel sizes are used in the same band.

Conclusion

The argument in subject should also be carefully taken into account before drawing conclusions on the study.

1 IntroductionThis contribution responds to an action item taken during the first Conf-Call and not yet fulfilled.

We still remain much dubious about the effective spectrum efficiency improvement of asymmetric deployment.

Nevertheless, for the study in subject, it was not yet clarified how the go/return coupling of the asymmetric channels could be done.

ECCElectronic Communications Committee

CE

PT

1

The coupling method affects the actual duplex separation of local TX and RX in each radio terminal; this has some impact on the equipment design.

Complete freedom choice of go/return frequencies is not advisable because of the too large possible variance of the TX/RX duplex separation and consequent impact on HW design.

We believe that also an efficient frequency coordination process would need some more definite rule limiting such variability within appropriate confines.

2 Equipment HW design impactIn modern equipment the generation of radio frequency in TX and RX local oscillators is obtained through synthesisers capable in general of generating all frequencies needed for a certain band arrangement.

In most cases TX and RX frequency generation is separately achieved1 (Note).

However, the required decoupling between local TX/RX (spaced by a duplex frequency) imply that in most cases the duplex filters cannot be effectively designed for covering a whole channel arrangement in a single implementation. In most cases, each channel arrangement is covered by few different filters, each modularly covering a number of (symmetric) channels.

If the constancy of duplex fails for desired asymmetry, the above design concept should be revised and the presently few different filters would increase in number as far as the duplex variance does.

It is well known that the increase of HW version automatically imply increase of cost and delivery time.

It is therefore of importance that the duplex frequency variance is kept at minimum or, at least, be clearly defined.

Last but not least, assuming that the “symmetric” deployment will maintain dominant (or considerable) status, it would be of high importance that

3 Channel arrangement impactBesides the above “equipment” impact, it is also expected that a spectrum efficient coordination can be done only when some appropriate rules for the TX/RX channels coupling are defined.

Complete TX/RX freedom in densely coordinated networks would certainly impair efficiency (this was the reason why our ancestors invented the “radio frequency channel arrangements”).

Therefore, this contribution analyses three example of possible “asymmetric usage” of present “symmetric” arrangements.

It should be noted that the examples are “simplified” assuming that only two channel sizes with 1/2 asymmetry are used. Obviously, if the asymmetry ratio would also be more variable, the complexity of the argument would also increase.

Figure 1 shows a generic channel arrangement where a number (e.g. 6) of larger channels (e.g. 28 MHz) is subdivided in doubled number (e.g. 12) of smaller channels 1/2 size (e.g. 14 MHz). It will be the basis for further considerations. The constant duplex spacing (DS) is also shown.

1 It should also be taken into account that, in some cases, the constant duplex permits some reduced complexity in RX frequency generation by simply “shifting” the TX one. This might not be applicable any longer.

28 MHz plan

14 MHz plan 1 2 3 4 5 6 7 8 9 10 11 12 1' 2' 3' 4' 5' 6' 7' 8' 9' 10' 11' 12'

2'1 2 3 4 5 6 1' 3'

DS

DS

4' 5' 6'

Figure 1: Example of conventional symmetric channel arrangement (6 x 28 MHz; 12 x 14 MHz)

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3.1 Asymmetry Example 1: Using both 14 and 28 MHz go/return within the same wider channel

This is the simplest way of using asymmetry; no specific subdivision of the band for wider and narrower channels.

The coordination of narrower “return” channels has only two choices within the same wider return channel.

1. The duplex variation is limited: DSasym = DS ± 7 MHz

2. Equipment HW of conventional “symmetric” systems is likely the same of “asymmetric” ones.

3. Impact on channel arrangement negligible.

4. The possible efficiency improvement is to be verified (the reuse of the unused 14 MHz return channels seems problematic).

3.2 Asymmetry Example 2:Subdivision of wider and narrower channels in different portion of the band

This example uses the approach sometimes applied by administrations of subdividing the band for wider and narrower channels use. This follows the principle that coordination among equal size channels is, in principle, more efficient.

Subdividing the band in equal number of 28 and 14 MHz paired channels, their go/return coupling shows:

1. The duplex variation is large: DSasym = DS ± 105 MHz (value depends on the actual number of available 28 MHz channels).

2. Furthermore, if we consider that the symmetric option should also be maintained, the result is still that any go channel should be possibly coupled with any (symmetric or asymmetric) return channel. Therefore, this is also against the original assumption.

3. Impact on channel arrangement is relatively low; only the “asymmetric” coupling becomes variable, the “symmetric” remains as the original arrangement.

4. The efficiency for the “asymmetric” operator is possibly better than example 3.1 (but to be checked) due to the homogeneous size channels zone. However, when another operator on the same area still use the “symmetric” approach they will use the same “go” but different “return” channels; the impact on the “global” efficiency is not known and should be verified.

1 2 3 4 5 6 7 8 9 10 11 12 1' 2' 3' 4' 5' 6' 7' 8' 9' 10' 11' 12'

DS(1-6) go = DS +- 7 MHz

DS(1'-6') return = DS +- 7 MHz

Example 1 of asymmetric use: 6+6 Channels with 1/2 asymmetry and mixed wide/narrow-band channels

1 2 3 4 5 6 1' 2' 3' 4' 5' 6'

9(5) 10(6) 11(7) 12(8) 9'(1') 10'(2') 11'(3') 12'(4')

DS(5) = DS - 105

DS(6) = DS - 91

DS(7) = DS - 77

DS(8) = DS - 63

DS(1) = DS + 105

DS(2) = DS + 91

DS(3) = DS + 77

DS(4) = DS + 63

3'(7') 4'(8')

Example 2 of asymmetric use: 4+4 Channels with 1/2 asymmetry in a narrow/wide channels band subdivision customary in some administrationsDS

1 2 3 4 1'(5') 2'(6')

3

3.3 Asymmetry Example 3

This example show the approach used by some administrations (mostly in the past) of confining smaller channels in the innermost part of the band.

Also in this case, subdividing the band in equal number of 28 and 14 MHz paired channels, their go/return coupling shows:

1. The duplex variation is reduced: DSasym DS 7 MHz to DS 49 MHz (value depends on the actual number of available 28 MHz channels). However, it should be first considered which would be the go/return coupling of “symmetric” channels. If it remains the conventional one (i.e. 1 1’ of 28 MHz) or also redefined (i.e. 1 3’, 2 4’ … of 28 MHz); in the second case the duplex variability would raise again and the HW commonality be also questionable.

2. Also in this case, depending on how the symmetric channels would be coupled, the equipment HW will be subject to less DS variation, but still hardly fulfilled with usual few version nowadays in use.

3. Impact on channel arrangement is high (we are not aware of any ECC Rec. or administration using this method)

4. The efficiency of the mixed symmetric/asymmetric network will be similar to example 3.2.

4 ConclusionsThe above discussion, even more shows that the adoption of an “asymmetric” arrangement usage, other than the simplest one shown in Example 1, raises a number of problematic to channel arrangements, network coordination (particularly when both symmetric and asymmetric links are used) and, last but not least, on the HW commonality between equipment used for symmetric and asymmetric applications.

This has to be taken into account in the study, with different evaluation of the network efficiency according the different arrangements used.

9 10 11 12 1' 2' 3' 4'

DS4 = DS - 49MHz

DS12 = DS - 7MHz

DS11 = DS - 21MHz

DS10 = DS - 35MHz

DS9 = DS - 49MHz

DS1 = DS - 7MHz

Example 3 of asymmetric use: 4+4 Channels with 1/2 asymmetry and separated wide/narrow-band channels (narrow in central portion of the band)

6' (12')1 2 3 4 3' (9') 4' (10') 5' (11')

DS2 = DS - 21MHz

DS3 = DS - 35MHz

4