When two or more cell-phones transmit data to the same network antenna channel at the same time, you often overhear other people’s conversations. Two Delft PhD-students have been working on receivers for GSM- and UMTS-networks that suppress this cross-talk.
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,,Our concept is revolutionising,” says Dr. Marco Moretti, from Italy, who worked on the concept during his PhD-project at the TU’s Telecommunications and Traffic-control Systems Group, supervised by Dr. Gerard Janssen. ,,Mobile phone companies paid lots of money for the UMTS-frequencies to extend their network capacity, and now I and others have shown that you can still almost double the capacity of the current GSM-network, which currently has more than 500 million users.”
The basis of Moretti’s concept is this: Have two cell-phones (instead of just one) transmit data at the same frequency at the same time to a mobile phone company’s base station antennae. This makes it possible to double the capacity of the network. Presently, when telephoning via a GSM-network, the base station instructs your phone to transmit its signals at a certain frequency, sending it in 577 microsecond packages, during one of eight timeslots. The antenna never receives two signals at the same frequency at the same time, so you’ll never overhear someone else’s conversation.
Moretti’s wanted to build a multi-user receiver, without introducing cross-talk. The trick, Moretti says, is to let the base station’s antenna assign the same timeslot to a mobile that’s close to the antenna and to a mobile that is further away. ,,Thus, one signal is always stronger than the other,” Moretti explains. ,,You then first try to detect the strongest signal.” By subtracting this signal from the total signal, the weakest signal appears.
,,Companies could build a system on this concept,” he says, adding that only the base stations’ software and hardware must be changed, not the cell-phones themselves.
Party
,,Most money is currently invested to overcome constraints in the UMTS-technology,” Moretti says. ,,But I think there might also be a future for an upgraded GSM, like GPRS, because UMTS is a very complex technique.”
Moretti’s colleague, Dr. Marco Hernandez, from Mexico, agrees that UMTS (Universal Mobile Telecommunications System)the standard for 3rd generation wireless communicationis complex to implement: ,,However, transferring data from the Internet through a GSM-network is very slow, so you need UMTS.” Hernandez and Moretti were both part of the same multi-user receiver project, sponsored by STW, a Dutch organisation that finances applied science projects.
,,When I started my PhD-project the expectations for 3rd generation mobile communication were high,” says Hernandez. ,,In theory, developing techniques for sending a video to someone%s cell-phone through UMTS isn’t that difficult. People did however underestimate how to jump from this theory to a real system. A completely new wireless network must be introduced, a giant technological and financial challenge, but most telecommunication companies face huge debts.”
However, there’s no way back, according to Hernandez: ,,In the USA, 3G services should be introduced this year or next. In Europe, I don,t dare to predict anything.” In UMTS networks, both the cell-phones and base stations transmit data at the same time and in the same frequency bandwidth. By assigning a different spreading code to every user, their information can be recovered at the receiver. ,,It’s like being at a noisy party and wanting to hear your friend’s voice, but he’s on the other side of the room. So you try to tune into his voice. My research on advanced receivers tries to mitigate the noise in the party as much as possible, enhancing the voice of my friend.”
With his iterative multi-user receiver, the desired user signal is initially decoded. This is a poor estimation, which is fed back into the system and after some iteration, the noise and interference are reduced to nearly zero. ,,It’s like a wizard has frozen all the people and noise of the party, except for me and my friend on the other side of the room, allowing us to finally communicate.”
Other researchers have also proposed the same kinds of receivers for UMTW, according to Hernandez. They won’t be implemented in the coming years, however. ,,Our technique is less complex and works better,” Hernandez claims, ,,but companies always prefer proven technologies%even though our new technique is cheaper.” So, a technique invented in 1998 will be implemented in the coming years. Hernandez% technique, however, was not invented until 2000.
When two or more cell-phones transmit data to the same network antenna channel at the same time, you often overhear other people’s conversations. Two Delft PhD-students have been working on receivers for GSM- and UMTS-networks that suppress this cross-talk.
,,Our concept is revolutionising,” says Dr. Marco Moretti, from Italy, who worked on the concept during his PhD-project at the TU’s Telecommunications and Traffic-control Systems Group, supervised by Dr. Gerard Janssen. ,,Mobile phone companies paid lots of money for the UMTS-frequencies to extend their network capacity, and now I and others have shown that you can still almost double the capacity of the current GSM-network, which currently has more than 500 million users.”
The basis of Moretti’s concept is this: Have two cell-phones (instead of just one) transmit data at the same frequency at the same time to a mobile phone company’s base station antennae. This makes it possible to double the capacity of the network. Presently, when telephoning via a GSM-network, the base station instructs your phone to transmit its signals at a certain frequency, sending it in 577 microsecond packages, during one of eight timeslots. The antenna never receives two signals at the same frequency at the same time, so you’ll never overhear someone else’s conversation.
Moretti’s wanted to build a multi-user receiver, without introducing cross-talk. The trick, Moretti says, is to let the base station’s antenna assign the same timeslot to a mobile that’s close to the antenna and to a mobile that is further away. ,,Thus, one signal is always stronger than the other,” Moretti explains. ,,You then first try to detect the strongest signal.” By subtracting this signal from the total signal, the weakest signal appears.
,,Companies could build a system on this concept,” he says, adding that only the base stations’ software and hardware must be changed, not the cell-phones themselves.
Party
,,Most money is currently invested to overcome constraints in the UMTS-technology,” Moretti says. ,,But I think there might also be a future for an upgraded GSM, like GPRS, because UMTS is a very complex technique.”
Moretti’s colleague, Dr. Marco Hernandez, from Mexico, agrees that UMTS (Universal Mobile Telecommunications System)the standard for 3rd generation wireless communicationis complex to implement: ,,However, transferring data from the Internet through a GSM-network is very slow, so you need UMTS.” Hernandez and Moretti were both part of the same multi-user receiver project, sponsored by STW, a Dutch organisation that finances applied science projects.
,,When I started my PhD-project the expectations for 3rd generation mobile communication were high,” says Hernandez. ,,In theory, developing techniques for sending a video to someone%s cell-phone through UMTS isn’t that difficult. People did however underestimate how to jump from this theory to a real system. A completely new wireless network must be introduced, a giant technological and financial challenge, but most telecommunication companies face huge debts.”
However, there’s no way back, according to Hernandez: ,,In the USA, 3G services should be introduced this year or next. In Europe, I don,t dare to predict anything.” In UMTS networks, both the cell-phones and base stations transmit data at the same time and in the same frequency bandwidth. By assigning a different spreading code to every user, their information can be recovered at the receiver. ,,It’s like being at a noisy party and wanting to hear your friend’s voice, but he’s on the other side of the room. So you try to tune into his voice. My research on advanced receivers tries to mitigate the noise in the party as much as possible, enhancing the voice of my friend.”
With his iterative multi-user receiver, the desired user signal is initially decoded. This is a poor estimation, which is fed back into the system and after some iteration, the noise and interference are reduced to nearly zero. ,,It’s like a wizard has frozen all the people and noise of the party, except for me and my friend on the other side of the room, allowing us to finally communicate.”
Other researchers have also proposed the same kinds of receivers for UMTW, according to Hernandez. They won’t be implemented in the coming years, however. ,,Our technique is less complex and works better,” Hernandez claims, ,,but companies always prefer proven technologies%even though our new technique is cheaper.” So, a technique invented in 1998 will be implemented in the coming years. Hernandez% technique, however, was not invented until 2000.
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