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Article - We Want Voice!

As technology evolves, new communications standards are emerging and have come out. With the explosive growth of the Internet, demand for broadband data has increased enormously, and the wireless industry has focused on making products that claim to deliver more and more bandwidth.

However, while doing so, they have so obviously forgotten the main service that all carriers live on – voice communications. Mostly, the excuse is that there is VoIP technology – if you want voice, you can do it. However, VoIP is very likely not an appropriate solution to carrier-grade, high-capacity voice requirements, especially in wireless environments and mobile use scenarios. Here's why.


One - VoIP is inefficient

This may sound as a speculation, but let’s just look at numbers. In the IP protocol, the minimum IP packet size is 78 bytes, because of the IP and Ethernet header information.

Suppose we use g.729 codec for voice transmission, which uses an 8 Kbps code rate and generates a voice frame every 10ms. So now, every voice frame contains just 10 bytes but the minimum IP packet size is 78 bytes. If we consider the efficiency of such transmission, it is in fact 10/78=12.8%. Pretty inefficient - based on this, sending an 8 Kbps stream requires about 64 Kbps of real bandwidth.

In wireless applications, radio airlink is the most valuable resource. To efficiently do voice, 64 Kbps per call is a huge waste of capacity, especially that each call will actually require even more – radio link overheads, retransmissions can easily double the radio resource consumption.

In landline networks such as Fiber and DSL, bandwidth consumption may not be an issue since they have a lot of capacity. For wireless operators on the other hand, capacity is a limited, precious resource.

Given those figures, standard Voice over IP technology is not the answer to offering carrier-class, high capacity voice. The strain is not only on wireless last mile links – the backhaul (transmission between sites) is also loaded, necessitating costly capacity upgrades.


Two - New Radio Technologies Neglect Voice

Older digital radio technologies, such as GSM and CDMA, were primarily designed for voice and make the best use of radio resources. Voice is by nature narrowband, so narrowband radio channels optimized for voice are highly efficient – some of the reasons for the success of GSM and CDMA for voice services.

Newer technologies are designed and optimized primarily for broadband data access. This is especially true for the OFDM/OFDMA radio schemes used by WiMax and LTE. OFDM divides the frequency bandwidth into smaller chunks, called sub-carriers. The orthogonality of the subcarriers (OFDM stands for Orthogonal Frequency Division Multiplexing) gives it good resistance to multipath, a common effect of non-line of sight deployment.

However, the issue is the granularity of those sub-carriers. Designed for broadband, they are relatively large in size – a few hundred kbps, and that sets the minimum possible data rate allocated to a single stream of data.

In LTE for example, the minimum resource size is 160 kbps. But then take a voice call. Even if it takes 64 kbps as explained above, now the minimum it must take is 160 kbps – so each voice call now requires 160 kbps, multiplied by 2 (since voice is bi-directional). A typical 5 MHz WiMAX or LTE carrier-sector will then only be capable of 24 simultaneous calls.

This inefficiency extends to not only voice calls, but other narrowband applications as well. Even for sessions that consume a small amount of bandwidth such as "chatty" Telnet/SSH, Remote Desktop etc. the inefficient air interface assigns a large resource chunk. This is essentially the main reason why broadband-type base stations such as WiMAX do not reach their optimal rated capacity under typical conditions. The Internet traffic is a mix of many types of broadband and narrowband applications, and the coarse resource management is extremely inefficient.

Such air interface inefficiencies are unacceptable in wireless networks. Overall network capacity is severely compromised, typically by a factor of 3.



Alloyant Technologies supplies high performance broadband wireless access systems designed for voice, data, SMS and full mobility support.