Eight-Channel DVB-C Direct VHF/UHF QAM A/C Modulator

Transcription

1 DirectQAM ¹) Module Technical Specification 10 may 2011 Version 1.1 Eight-Channel DVB-C Direct VHF/UHF QAM A/C Modulator MAIN FUNCTIONS Eight DVB-C modulators with agile output using the DirectQAM principle Two independent groups of four adjacent channels; Each group has independent settings for base RF frequency Gigabit-Ethernet interface for control and contribution of up to eight Transport Streams RF-mute function for fail-over switching NIT-replacement for localising a network FUNCTIONAL BLOCK DIAGRAM STN B.V ¹) Protected by worldwide patents Page 1 of 9 Specifications may change without prior notice!

2 APPLICATIONS Key component in next-generation HFC cable-tv IP networks. Cable-network emulator for development labs, repair shops, production testing, etc. CONTEXT A schematic representation of an HFC cable network with DirectQAM modules is shown below. The Headend receives TV programs from contribution links, assembles Multi-Program Transport Streams (MPTS), and multicasts these on the HFC IP network. The DirectQAM modules are located in the Nodes that feed the final coax to the homes. Each DirectQAM module receives 8 multi casted MPTS streams and trans modulates them to QAM. A key advantage of the concept is that the DirectQAM modules in each Node can be configured to select a different mix of streams. STN B.V. Page 2 of 9 Specifications may change without prior notice!

3 In order that the STB s perceive a consistent DVB network, the Headend generates Network Information Tables (NITs) and multicasts these in TS-over-IP format to the Nodes. Each DirectQAM module reads the appropriate Replacement NIT and inserts it into the MPTS streams. INPUT / OUTPUT / INDICATORS RJ-45 Gigabit ruggedized Ethernet port F-Type RF Output Power (connector type DB9) 4x LED Power On (green) Device Error (red flashing) Ethernet link status Ethernet activity NETWORK CONNECTION Min Typ Max Unit GIGABIT ETHERNET PORT Standard IEEE 802.3af Data Rate 1000 Mbps Connector RJ-45 PROTOCOL TS Encapsulation Pro-MPEG CoP #3 release 2 Modes UDP; no RTP, no FEC Transport Packets / IP Packet 1 7 Latency (excluding jitter 10 ms tolerance) CONTROL Multicast Support IGMP v2 Network Management SNMP v2c Time/Date Synchronisation (S)NTP For log timestamps NIT REPLACEMENT Size of NIT Buffer 10 kbyte STN B.V. Page 3 of 9 Specifications may change without prior notice!

4 RF SPECIFICATIONS Min Typ Max Unit DVB-C MODULATION Standard EN Constellations 64 or 256 QAM Symbol Rate Ms/s fixed MER 44 db Spectrum Flatness ±0,2 db Shoulder Attenuation 55 db RF OUTPUT Impedance 75 Ω Return Loss db Connector Type F female Level (per QAM Channel) See table on bottom of page Step Size 0.5 db Accuracy ±1 db RF-Off Attenuation 70 db Spectral Purity -60 dbc /-3dBm ref Wideband Noise dBm/QAM channel level RF FREQUENCY Range MHz Step Size 12.5 khz Stability 5 ppm Accuracy 5 ppm Phase 10 khz -98 dbc/hz RF level conversion table dbmw//75ω dbmv dbµv STN B.V. Page 4 of 9 Specifications may change without prior notice!

5 OTHER SPECIFICATIONS Min Typ Max Unit POWER Power Supply 12 V +- 5% Power Consumption 12 W ENVIRONMENTAL Temperature Range C REGULATIONS EMC CE Industrial MECHANICAL Dimensions W x H x D 100x160x18 (PCB Only) mm 107x163x32 (Boxed version) PRODUCT FUNCTIONS The DirectQAM module features eight complete DVB-C modulators, organised in two groups of four. All eight modulators are operated at the same symbol rate and same input-to-output latency. Per group of four an independent base frequency and channel spacing can be specified. Every channel can be switched on or off individually. The module gets Transport-Stream data by real-time reception of up to eight UDP streams. For each stream an independent IP address and port address can be specified. The joining of multicast groups is supported. The UDP packets are unpacked into Transport Packets, which are stored (conceptually) in a FIFO buffer. The network will incur variable delay (jitter) on the UDP packets. The DirectQAM module measures the arrival time of the UDP packets and applies a smoothing algorithm to the timestamps by using a linear regression algorithm. The result is an estimate of what the arrival time would have been without network jitter. A secondary result from this process is an estimate of the Transport Rate. An intentional delay is added to the dejittered timestamps before releasing the Transport Packets from the FIFO. The delay corresponds to the maximum amount of jitter that can be tolerated in the arrival of the UDP packets. The so-recovered Transport Stream is re multiplexed to a fixed rate that matches the symbol rate and modulation settings. Re multiplexing in this context requires null packet insertion and PCR correction. The resulting TS is modulated in accordance with the DVB-C standard by applying PRBS, Reed-Solomon FEC, Interleaving, QAM mapping and channel filtering. Finally the signal is fed into a direct digital I/Q modulator for generating the modulated signal in the MHz range. The modulated signal is led through an RF output amplifier with programmable gain and regulation loop, resulting in a cumulative output level between -14 and +6dBm at 75Ω. STN B.V. Page 5 of 9 Specifications may change without prior notice!

6 NETWORKING Each DirectQAM module has a unique MAC address sequentially assigned from a MAC address range provided to STN. Note: next to the unique MAC address each DirectQAM module has an independent unique serial number. The IP address will be fixed, DHCP is not supported. The fixed IP address can be configured using a configuration tool. No factory reset of the IP address is available; the configuration tool will always be able to reconfigure the IP address regardless of the programmed value. The IP-address configuration process works with a laptop and the DirectQAM module connected directly to each other in a mini-network. A proprietary protocol is used as follows. The configuration tool broadcasts a UDP message. The NIT-REPLACEMENT A special function supported by the DirectQAM module to enhance deployment options is NIT replacement. The NIT in each Transport Stream can be replaced by a NIT selected from an independent NIT stream. The intention is to allow localization of the NIT-actual. A similar function for the NIT-other is not supported. An IP address and PID can be programmed to identify a multicasted Transport Stream containing the replacement NIT. The DirectQAM module reads Transport Packets from the selected PID and caches the NIT table internally. Just a single NIT can be cached; The same NIT will be used for all channels. NIT replacement can be enabled individually for each of the eight channels. If NIT replacement is disabled, or if it is enabled but no complete NIT has been received yet, Transport Packets with PID 16 (NIT PID) are unaffected. DirectQAM module reacts with an UDP packet containing its current IP address and MAC address. After that the configuration tool sends a UDP packet to the DirectQAM module to configure the IP address, subnet mask and default gateway. These settings are persisted in flash memory. Run-time network configuration includes nine programmable multicast IP address/port filters, eight for the QAM channels and one to receive a NIT for the NIT-replacement function. The DirectQAM module joins multicast groups using IGMP v2. Source-specific multicasting (requiring IGMP v3) is presently not supported but the MIB is prepared for this as a future extension. If NIT replacement is enabled and a complete replacement NIT has been received, then each packet with PID 16 is replaced by a packet from the replacement PID. The continuity counter of the packets is automatically incremented for each packet. Please note that it is not required that PID 16 in the channel s Transport Stream contains a NIT. PID 16 may consist entirely of null packets, too. Furthermore, if PID 16 does contain a NIT, the repetition rate of the replacement NIT may be different from that of the original NIT because of a difference in number of packets. While cycling the replacement NIT, the DirectQAM module keeps monitoring the NIT-replacement IP address to check whether a NIT with a new version number is available. If so, a new replacement NIT is downloaded, but the old one is still being scheduled. STN B.V. Page 6 of 9 Specifications may change without prior notice!

7 When the entire new replacement NIT has been downloaded, the DirectQAM module starts scheduling the new NIT. DEVICE MANAGEMENT & CONTROL The product can be managed and controlled with a web interface and through SNMP (for a network management system). Both interfaces give access to all control settings, status information, alarm status and the log. The main purpose of the web interface is product configuration and getting diagnostics for troubleshooting. SNMP, the industry-standard network-management protocol, is intended for operational control. STN B.V. Page 7 of 9 Specifications may change without prior notice!

8 The table below provides an overview of interface. Further details can be found in the management and control information the detailed specifications. available over the web and SNMP Control parameters per stream IP Address / Port Channel enable IPV4 address and port number; may be unicast or multicast Channel is used yes/no Monitoring per stream Delay factor Maximum delay factor (indicator for IP jitter) in the last 10 seconds TS rate TS rate as estimated by the DQAM module Control parameters per group of 4 channels Modulation Annex-A* (ITU-T-J83) standard Annex-B Option Annex-A and Annex-C not available for B firmware. Annex-C* Constellation 64, 256 Number of QAM constellation points: 64, 256 Base frequency MHz Centre frequency of first channel in the group Channel spacing 5.. 8MHz Channel spacing between adjacent channels Device-wide control parameters Symbol rate 5.05/5.36 Mbd Symbol rate in with a resolution of 1 bd Jitter tolerance ms Amount of IP jitter that can be tolerated without corrupting the outgoing TS (underflow/overflow of internal buffer). The jitter tolerance (necessarily) will add up to the input-to-output delay RF enable Enable output signal at RF output RF level dbm Level at RF output with 0.5dB steps (see table on page 4) NIT address / port IPV4 address and port number of replacement NIT NIT PID PID from which to get replacement NIT NIT replace enable (S)NTP server Device-wide monitoring Time Enable NIT replacement Enable NIT replacement Current time recovered through (S)NTP Log 256 entries Logs all settings, alarms and reboots Output level dbm Output level actually measured Temperature C Ambient temperature Standard MIBs MIB II Alarms RF level Temperature System, Interfaces, at, ip, icmp, tcp, udp, egp, snmp Unable to regulate RF level to the desired level Device temperature exceeds a programmable threshold STN B.V. Page 8 of 9 Specifications may change without prior notice!

9 Whenever a setting is applied that may cause unwanted noise on the output (e.g. because of DAC reconfiguration), the RF output will be muted to avoid pollution of the entire band. Settings that cause such service interruptions will be clearly marked in the configuration manual. Any control setting applied through the web or SNMP interface is persisted in flash memory, so that when the device reboots after a power cycle it starts with the lastused settings. The RF level and temperature alarms are throttled to a maximum of one alarm per 5 minutes. If the alarm condition persists, the corresponding trap is generated once every 5 minutes. LOGGING A log is maintained in flash memory to keep a persistent record of interesting events. The main purpose of the log is to facilitate post-mortem fault analysis. Each log line will be time stamped with the current date/time, which is synchronised through NTP. When the date/time has not been synchronised yet, MISCELLANEOUS When the DirectQAM module boots some elementary consistency checks will be applied, but no sophisticated self-test. The DirectQAM module will employ a watchdog to automatically restart the device upon a software crash. The product s firmware and software can be uploaded via the web interface using ftp. The first version of the DirectQAM the number of seconds since last reboot is used instead. The log will keep track of the following events: o Device started o NTP lock achieved o Any control setting applied o SNMP traps module will not implement a sophisticated mechanism to authenticate the uploader. A dual-bios architecture is used to avoid disasters when a bad image would be uploaded. The DirectQAM firmware shall be protected by a simple Intellectual- Property copy protection mechanism. STN B.V. Page 9 of 9 Specifications may change without prior notice!