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Capacity Optimization for CDMA Networks
Ditech Networks’ innovative CDMA Capacity solution enables carriers to optimize the forward-link capacity of
existing CDMA networks, maximizing the value of network equipment.
This solution features Ditech’s Voice Quality Assurance (VQA™) software, which also significantly improves the end-user
listening experience by providing background noise reduction, acoustic echo control, background noise compensation, and
speech enhancement.
Overview
CDMA and Background Noise
As the number of CDMA subscribers grows and average minutes per month increase, more and more mobile calls originate
and terminate in noisy, urban environments. The background noise does more than degrade voice quality — it also impacts
network capacity. CDMA’s Rate Determination Algorithm (RDA) is designed to select Rate 1 (9.6 kbps) for speech and
Rate 1/8 (1.2 kbps) for non-speech. Unfortunately, impairments such as background noise and acoustic echo are often
misinterpreted by the RDA as voice, consuming unnecessary network bandwidth.
Realizing CDMA Capacity
Ditech’s bidirectional noise cancellation leads the industry with advanced multi-band spectral processing that adaptively
reduces all forms of noise by up to 21 dB. Ditech’s acoustic echo cancellation automatically removes all forms of acoustic
echo with delays from 0 to 400 ms in both directions, providing maximum performance in today’s converged networks.
When deployed at the MSC, Ditech’s CDMA Capacity solution prevents noise and acoustic echo from entering the RDA,
reducing the average forward-link data rate generated by the vocoder by an average of 20% in noisy conditions.
Figure 1 illustrates how Ditech’s solution influences the Rate selected by the RDA in the Enhanced Variable Rate
Codec (EVRC). |
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Ditech Platforms
Ditech’s CDMA Capacity solution is available on the following platforms:
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Figure 1 – Illustration of Noise and Acoustic Echo Reduction and Selected Rate
Bit Rate Reduction and Increased Capacity
Figure 2 shows the distribution of Rates 1, 1/2, and 1/8 measured during live EVRC network tests in noisy
conditions with and without VQA technology.
Figure 2 – Typical Effect of VQA Technology on Forward-Link Bit Rate
In these tests, the average bit rate was reduced from 6.9 to 5.5 kbps – a 20% reduction – which,
as shown in Figure 3, corresponds to a 25% capacity increase. In field deployments in noisy conditions, Ditech
typically improves forward-link capacity by 10% to 30%.
Figure 3 – Bit Rate and CDMA Capacity [Source: Andrew Viterbi and Vijay K. Garg]
Improved Voice Quality
In addition to the capacity benefit, Ditech’s VQA technology improves overall voice quality by removing background
noise and acoustic echo, and by improving speech clarity with features such as Enhanced Voice Intelligibility. In
live CDMA network trials where subscribers were asked to make and evaluate large numbers of phone calls, VQA
technology significantly improved voice quality by an average of 0.4 MOS points, as shown in Figure 4.
Improved voice quality can facilitate the migration of voice traffic to wireless networks and drive
additional revenue, as well as differentiate service from competitors.
Figure 4 – Effect of VQA Technology on Mean Opinion Score (MOS)
| Features Providing Capacity Optimization |
Noise Cancellation
Reduces background noise without suppressing voice volume to improve the sound quality of calls.
Industry-Leading Performance: Advanced multi-band spectral processing techniques remove up
to 21 dB of noise during both speech and pauses, providing a dramatic increase in quality for calls placed from
noisy environments.
Bidirectional Operation: Operates in both uplink and downlink directions simultaneously, providing
excellent speech quality for both parties.
Excellent Speech Quality: Advanced noise suppression techniques function only when noise is present,
resulting in excellent clean speech performance with no speech degradation.
Rapid Convergence: Dynamically adapts to changes in noise spectrum, in real time, converging or
re-converging in less than 200 ms.
Enhanced VAD Post-Processor: Unique two-pass algorithm provides an extremely accurate determination
of speech vs. noise, providing excellent noise reduction performance under all noise conditions.
SNR Adaptive Noise Cancellation: Automatically adjusts noise reduction performance to match changing
noise levels, providing callers with consistent noise reduction for both tandem (on-net mobile to mobile) and off-net
(mobile to PSTN) calls.
Adjustable Noise Floor: Spectrally-matched comfort noise can be customized by the operator to provide
high or low levels of residual comfort noise in accordance with subscriber preferences.
Frame Loss Handling: Voice quality enhancement features automatically accommodate for frame erasure
in wireless networks to ensure consistent sound quality before and after the loss condition.
Acoustic Echo Control
Addresses the echo that is common from handsets and handsfree units.
Bidirectional Echo Cancellation: Unique bidirectional solution removes acoustic echo from both
near- and far-end sources, resulting in excellent conversational quality for both parties.
Industry Leading Performance: Selectable WAEPL from 45 dB to an industry-leading 15 dB ensures
protection from even the strongest echo sources, while maintaining excellent double-talk performance.
Converged-Network Ready: Effectively removes acoustic echo with delays up to 400 ms in each
direction, providing maximum performance for wireless, wireline, and VoIP environments.
Adaptive Delay Mode: Automatically adjusts to actual detected delay on a per-call, per-channel
basis, avoiding the need to configure a fixed bulk delay for each channel in advance.
Spectral Comfort Noise Match: Automatically generates comfort noise to match actual background
noise levels and spectral characteristics, providing improved conversational call quality without an
annoying “dead air” effect. |
| Additional Voice Quality Features |
Enhanced Voice Intelligibility: Rebalances spectral signature
when listening in noisy conditions, improving understanding of the human voice.
Adaptive or Dynamic Level Control: Provides optimal response to any network voice level condition and listening environment.
Experience Intelligence™ (EXi): Provides continuous, non-intrusive measurement and reporting of
a full range of voice quality metrics on every call.
See the VQA Overview for more information on these additional features.
Ditech also has CDMA solutions that include Hybrid Echo Cancellation (HEC).
Please contact us for more information. |
