Mobile Blog: Video, Media, Augmented Reality, Rich Media, IVVR

3G systems were designed with the notion of enabling a single global standard to fulfil the needs of anywhere and anytime communication (Etoh). Compared to 2G (Second generation mobile networks, services and technologies) systems, 3G systems focus more on multimedia communication such as video conferencing and multimedia streaming. ITU (International Telecommunication Union) defined IMT-2000 as a global standard for 3G wireless communications and, within this framework, 3GPP (3rd Generation Partnership Project) developed UMTS (Universal Mobile Telecommunications System) as one of today

photo credit: dno1967

3G video telephony generally operates over a single 64 kbit/s connection where both parties need to share the available bandwidth. Effectively, the application then is left with 60 kbit/s, or less that are dedicated for both media types, since H.245 call control messages reduce the gross bandwidth. In 3G-324M systems, the bandwidth is allocated dynamically; however, generally said, every party has 50% of the bandwidth available for sending audio and video signals. In a typical unidirectional scenario, 12.2 kbit/s are allocated for the speech codec, and a bitrate of 43-48 kbit/s is allowed for the video data (Sang-Bong, Tae-Jung and Jae-Won).

By employing rate control methods in the media encoders, the network can dynamically change these bitrates depending on network conditions and application demand. When two parties communicate simultaneously, the bitrates for the speech and video codec can be reduced in the encoders of both parties, keeping the overall bitrate below 64 kbit/s. For instance, when just one party shows speech activity, the speech bitrate for the other party can be reduced to a minimum where only comfort noise is generated on the receiver side (Holma and Toskala); AMR (Adaptive Multi-Rate) can perform these bitrate changes every 20ms. For video, the encoder can reduce the average bitrate by either reducing the frame rate or simply dropping frames during transmission. To increase the overall frame rate on the receiver side, the decoder can employ H.263 temporal scalability.

In 3G video telephony, the audio and video signals are bidirectionally streamed over dedicated circuit-switched W-CDMA (Wideband Code Division Multiple Access) paths. Streaming describes media is continuously being received or sent and played back on a terminal. Non-conversational one-way audio or video streaming requires a transport delay variation of below 2s (3GPP (3rd Generation Partnership Project)). In contrast, two-way video telephony introduces even higher real-time requirements with an end-to-end, one-way delay of below 150-400ms

photo credit: Tambako the Jaguar

Wie im IVVR (Interactive Voice & Video Response) Blog angek

photo credit: iboy_daniel

In the following I describe how the characteristics of wireless networks affect the audiovisual quality of 3G video telephony and especially IVVR (Interactive Voice & Video Response) applications. The impact of these characteristics need to be considered when designing IVVR applications and services:

Wireless networks are inherently error prone. Bitrates in wireless systems tend to fluctuate more as compared with wired networks. In wired networks, phenomena such as fading, shadowing, or reflection are non-existent so that, for the most part, the same bandwidth and much higher bandwidths are present during transmission. Influences on signal propagation cause the constant changing bandwidths in wireless systems. Generally, the receiving power depends on the distance between sender and receiver. The receiving power p decreases proportionally to the square of the distance between sender and receiver:

p=1/d²

where d is the distance between sender and receiver (Schiller).

Receiving power is influenced further by frequency dependent fading, shadowing, reflection at large obstacles, refraction depending on the density of the medium, scattering at small objects, and diffraction at edges.

The effect of multipath propagation can cause jitter when the radio signal reaches the receiver by two or more paths at different times. Moreover, the mobility of the user adds another set of problems that results in fading of received power over time; the channel characteristics change over time and location. This exacerbates the effect of multipath propagation because signal path change will be increased as the user changes his or her location. Changes in the distance between sender and receiver cause different delay variations of different signal parts.

The phenomenon of

photo credit: jepoirrier

I just posted my article about the IVVR (Interactive Voice & Video Response) Game Santa Claus Sleigh Ride, and I totally forgot to post the number where you can play the game by yourself.

You can give it a try by placing a video call to +498938155555. You can probably only reach it within Germany. But I haven’t tested this, though.

By the way: Do you know more IVVR servics, either in Germany or worldwide? Use the comment function to post them and I will create a list of IVVR services!