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A fiber optic node has a broadband optical receiver, which converts the downstream optically modulated signal coming from the headend or hub to an electrical signal going to the customers. As of 2015, the downstream signal is a RF modulated signal that typically begins at 50 MHz and ranges from 550 to 1000 MHz on the upper end. The fiber optic ...
Downstream: All versions of DOCSIS prior to 3.1 specify that 64-level or 256-level QAM (64-QAM or 256-QAM) be used for modulation of downstream data, using the ITU-T J.83-Annex B standard [16] for 6 MHz channel operation, and the DVB-C modulation standard for 8 MHz (EuroDOCSIS) operation. DOCSIS 3.1 adds 16-QAM, 128-QAM, 512-QAM, 1024-QAM, 2048 ...
For example, if the cable modems on every service group use 24 channels for downstream, and 2 channels for upstream, then 3 downstream connectors can service the cable modems on two service groups, and be serviced by 1 upstream connector. [5] A service group may serve up to 500 households.
If necessary, an optical amplifier can be used to boost the downstream optical signal to cover a greater distance. The fiber-optic micro-nodes – which are also referred to as RFoG optical-networking units (R-ONUs) – terminate the fiber connection and convert traffic for delivery over the in-home network.
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Example 5: The downlink of a V.92 modem uses a pulse-amplitude modulation with 128 signal levels, resulting in N = 7 bit/symbol. Since the transmitted signal before passband filtering can be considered as baseband transmission, the spectral efficiency cannot exceed 2N = 14 (bit/s)/Hz over the full baseband channel (0 to 4 kHz). As seen above, a ...
Comparison of mobile Internet access methods Common name Family Primary use Radio tech Downstream (Mbit/s) Upstream (Mbit/s) Notes HSPA+: 3GPP: Mobile Internet: CDMA/TDMA/FDD MIMO: 21 42 84 672: 5.8 11.5 22 168: HSPA+ is widely deployed. Revision 11 of the 3GPP states that HSPA+ is expected to have a throughput capacity of 672 Mbit/s. LTE: 3GPP ...
For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt . In broadcasting terminology, 1 mV/m is 1000 μV/m or 60 dBμ (often written dBu). Examples. 100 dBμ or 100 mV/m: blanketing interference may occur on some receivers