6.	Supplement No.30 (new)



Recommendation G.173



TRANSMISSION PLAN ASPECTS OF LAND MOBILE TELEPHONY NET-
WORKS



	(This Supplement is proposed for study during the present study period with the aim 
of converting it into a Recommendation.)



1.	General



	This Recommendation is primarily concerned with the special planning aspects 
which pertain to analogue or digital land mobile systems. Such systems, due to 
technical or economic factors, will prevent a full compliance with the general char-
acteristics of international telephone connections and circuits recommended by 
CCITT.



	The scope of this Recommendation is thus to give guidelines and advice to adminis-
trations as to what kind of precautions, measures and minimum requirements which 
are needed for a successful incorporation of such networks in the national PSTN.



	The performance objectives of such systems may vary between different groups of 
customers. For normal customers the objective should be to reach a quality as close 
as possible to CCITT standards. For other groups of very disciplined customers, 
other performance objectives might be acceptable.



2.	Network configurations



	Under study.



	Under this headline administrations should be advised to use four-wire transmission 
to avoid problems when accessing inherently four-wire mobile links.



3.	Nominal transmission loss of mobile links



	Under study.



	Under this headline the problems with the application of loudness ratings and the 
correct loading of the radio channels should be discussed.



	The recommended LR values in CCITT RecommendationG.121 are not directly 
applicable due to the fact that the background noise level is higher in a car than that 
assumed in RecommendationG.121.



	What is the design objective for the speech levels from the radio path and what lev-
els should be delivered to the network?



4.	Stability



	Under study.



5.	Echo



	Under study.



	Under this headline the need for echo control devices should be discussed.



6.	Noise



	Under study.



	(Can the European group give indications of the inherent noise performance of the 
codec algorithms being considered?)



7.	Delay



	Under study.



8.	Effects of errors in digital systems



	Several coding methods, such as SBC, ATC, RELP and APC-AB with transmission 
bit rates below 16kbit/s have been proposed to achieve spectrum utilization effi-
ciency and quality comparable with conventional analogue FM systems. However, 
the application of such highly efficient speech coding methods to land mobile radio 
can lead to a significant degradation in quality because of transmission errors.



	Mobile radio links are not always error-free. Burst errors occur frequently due to 
multipath fading. It has been reported that the average bit error rate (BER) perfor-
mance of diversity reception is 10-2-10-4 in the

10-20dB range of the average carrier-to-noise power ratio (CNR), and burst error 
length reaches 20-100bits in case of 16kbit/s digital signal transmissions. There-
fore, robustness against burst error is an important characteristic for speech coding 
applied to mobile communication. Speech CODECs in mobile radio links should 
involve error control techniques so as to provide robustness in multipath fading 
channels. Thus, the transmission bit rate includes redundancy bits for error control.



	Concerning quality evaluations, it may be better to use the average CNR as the 
receiving level for comparisons among analogue and digital systems. This is 
because it can present the receiving level as a normalized unit for both analogue FM 
and digital systems. In quality evaluations between digital systems, the average sig-
nal energy per bit to noise power density ratio (Eb/No) is suitable for the presenta-
tion of the receiving level. This is because it can describe the receiving level as a 
normalized unit for any transmission bit rate and receiving bandwidth.



9.	Quantizing distortion



	Under study.



10.	Effect of transmission impairments on voice band



	Under study.



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