Category: 4G Technology

What’s the Difference between TDD and FDD

Since 4G Technology is becoming more and more known, most people may know TDD or FDD, but may not know the difference between the two technology clearly. It’s obevious that FDD LTE network is more commonly deployed and launched to commercial. So what’s the advantage of FDD-LTE 4G network?

 

Before we introduce the compare TDD and FDD, let us simply introduce the communication system. Depending on whether two sides could simultaneously transmit data, there exist three transmission techniques:

First one is Simplex, which means one party transmits to the other party; the other party can only receive it and can’t transmit data simultaneously. There is only one frequency spectrum used. The traditional radio(non-interactive) and television is just this communication method.

Second one is Half Duplex, which means both party in two sides could transmit and receive data, but not at the same time. There is only one frequency (channel) used, but there are two ways. Walkie-talkies or other two-way radio systems are this communication method application.

 

Third one is Duplex, which means both party in two sides could transmit and receive data simultaneously, The communication is two-way and two frequencies (channels) are used – one for transmitting and one for receiving.

From above introduction, it’s clear that Duplex is the most efficient communication system. The providers all over the world upgrade their network from 2G GSM to 3G UMTS, and now to 4G LTE or WiMAX, which is just to improve the communication efficiency. That’s why the 4G LTE FDD and TDD were born.

FDD, the abbreviation of Frequency Division Duplexing, stands for the communication is done on only one frequency, but the transmitting and receiving data are at different time. This method of communication is using Half Duplex system.

TDD, the abbreviation of Time Division Duplexing, stands for the communication is done on two independent frequencies and the transmitting and receiving data are simultaneous. It’s typical Duplex communication system.

 

The advantage of TDD could obviously come into reflect when the uplink and downlink data transmissions are not symmetrical. A typical disadvantage of TDD is the need to use guard periods between the downlink and uplink transmissions. So if downlink and uplink are both busy, TDD may great pressure for data transmission.

 

The advantages of FDD are typically observed in situations where the uplink and downlink data transmissions are symmetrical (which is not usually the case when using wireless phones). More importantly, when using FDD, the interference between neighboring Radio Base Stations (RBSs) is lower than when using TDD. Also, the spectral efficiency (which is a function of how well a given spectrum is used by certain access technology) of FDD is greater than TDD.

In fact, the two LTE versions TDD and FDD are very similar, just the physical layer are different. So the UEs could support both of TD-LTE and FDD-LTE with only one chipset, which can come true based on only minor modifications. So the mobile broadband with the chipsets below will be able support both LTE TDD and FDD.

  1. ST-Ericsson (M700/M710 chipsets)
  2. Altair Semiconductor (FourGee-6150 chipset)
  3. Qualcomm (MDM9200/MDM9600 chipsets)

And per the official information, HUAWEI E392 and E398 are both the UEs which could support TD-LTE and FDD-LTE model. But with different version, some of them may only support single version.

Conclusions

FDD is an older scheme that was best suited for applications, such as voice, that generate symmetric traffic, while TDD is best suited for bursty, asymmetric traffic, such as Internet or other datacentric services.

* In TDD, both the transmitter and receiver operate on the same frequency but at different times. Therefore, TDD systems reuse the filters, mixers, frequency sources and synthesizers, thereby eliminating the complexity and costs associated with isolating the transmit antenna and the receive antenna. An FDD system uses a duplexer and/or two antennas that require spatial separation and, therefore, cannot reuse the resources. The result is more costly hardware.

* TDD utilizes the spectrum more efficiently than FDD. FDD cannot be used in environments where the service provider does not have enough bandwidth to provide the required guardband between transmit and receive channels.

* TDD is more flexible than FDD in meeting the need to dynamically reconfigure the allocated upstream and downstream bandwidth in response to customer needs.

* TDD allows interference mitigation via proper frequency planning. TDD requires only one interferencefree channel compared with FDD, which requires two interference-free channels.

* In summary, TDD is a more desirable duplexing technology that allows system operators to receive the most from their investment in spectrum and telecom equipment, while meeting the needs of each individual customer.

4G Broadband for 4G LTE Band 3 (1800Mhz)—Most Commonly Commercial LTE Spectrum

According to the most recent report of LTE network status from GSA, total 42 operators over the world had commercially launched LTE 1800Mhz as their next generation LTE network spectrum. Some of them may set this single band or as a part of multiple band deployment. In the total 113 commercial LTE networks, the band 1800 occupies 37%, which let it become the most popular and most commonly commercial LTE band.

And we also get the the spectrum of 1800Mhz is now available in follow 29 countries: Angola, Australia, Azerbaijan, Croatia, Czech Republic, Denmark, Dominican Republic, Estonia, Finland, Germany, Hong Kong, Hungary, Japan, Latvia, Lithuania, Mauritius, Namibia, Philippines, Poland, Portugal, South Africa, Saudi Arabia, Singapore, Slovak Republic, Slovenia, South Korea, Tajikistan, UAE, and UK.

It would be lucky for those people who had a 4G USB Modem, 4G WiFi Router, 4G Tablet or 4G Smartphone, because if they go to these countries, they just need to change their SIM card, they can easy enjoy the local 4G Service. Of course, they have to make sure their devices are unlocked. Here now most of the 4G broadband could find unlocked one in the market.

In this case, what’s the best 4G USB modem and 4G WiFi Router for band 1800Mhz? It’s a good question for those who usually go to different countries, this information help them to get  devices for commonly use.

 

Per the past market record, HUAWEI and ZTE sales of 4G LTE terminal leads the 4G era. And the two Chinese vendors released the most 4G gadgets. Unlike 3G USB modem or 3G Router, 4G modem and 4G Router are not in high price range because very few people feel urgent to use 4G broadband to get 4G speed, the production of these broadband in low level. And the current economy depression slower down the promotion of 4G.

Now we back to the question, what is the best 4G USB modem for spectrum 1800Mhz? The writer think to give options is better to give decision, HUAWEI is the world top telecom equipment supplier and their modems and routers are stable functions, but its competitor ZTE is also not bad, with the reliable quality, ZTE can offer comparatively better price than ZTE. Just like to choose a smartphone between Apple and Samsung, if you want more fashion and more cool, choose Apple, but if you concern more about the price, SAMSUNG may be a better choice.

So we recommend HUAWEI E392 4G LTE Surfstick and ZTE MF820 4G USB modem for band 1800Mhz. But you may feel confused by HUAWEI E392 model number, you can check the previous blog about E392 frequency and you can choose the right one.

 

Regarding the 4G Router, it seems HUAWEI E589 4G Pocket WiFi and ZTE MF91 4G Pocket WiFi Router are perfect, but per our investigation, Sierra Wireless released its 4G pocket WiFi Router in large quantity, it’s now selling at lower price, Sierra Wireless 760s and 762s 4G LTE Mobile Hotspot. People can take them into consideration.

How to Choose a 4G LTE USB Modem

More and more advertisements are introducing 4G to people, declaring a new era is coming. As a consumer, perhaps you may not concern what’s 4G or what is LTE, the top thing you want to know is what I can benefit from 4G. Great, that’s the key point. What can we benefit from 4G?

To explanation simply based on real life experience, you can download a HD movie of 2GB or more in few seconds, you can play complex online games without any interruption and you can transfer large file only a very short while. Yes, 4G can bring us fantastic speed! That’s why the providers are trying to promoting 4G, they finally want you guys to use their 4G devices. Of course, most of time, there would be contract with the devices and you are not free to use other SIM card.

 

But if you want to use unlocked broadband and SIM unlocked to any operators, how to choose the right model per the preference? Since the most popular 4G device from operator is 4G USB Modem with LTE technology, so we take 4G LTE USB Modem as example to explain, of course, unlocked. Then our question change to: How to choose a 4G LTE USB Modem?

 

Actually, to buy a 4G USB Modem, just like to buy a mobile phone. Most of the people would consider the brand, Apple, Samsung, HTC are well known and series of phones are optional for almost all the preference. And it’s not hard to determine. But for 4G USB Modem, it seems not that easy…It probably because most of the equipment suppliers are not as famous as the providers and the second reason is that the modems, routers, or other telecom equipments are printed the providers’ logos. Take Vodafone 4G LTE Surfstick K5005 as example, even though the users may use the surfstick for many years, they may don’t know it’s produced by HUAWEI and the HUAWEI factory model is HUAWEI E398.

 

So the first step to choose a 4G USB modem is to find which brand you prefer. If you don’t know, that would be better to make a decision. Follow me, I will guide you. Someone may ask, may I know how many brands there are all over the world? Ok, it’s time to share, most of us may know SAMSUNG Smartphone, but actually, SAMSUNG is also professional in network solution. So it also has 4G USB Modem available in the market. Some guys may feel good, ok, I like SAMSUNG, I choose it. Don’t be glad so early. After reading the full article, you may feel disappoint. Now I could tell you, SAMSUNG 4G LTE Surfstick is just for specific country and LTE frequency, so it may not be appropriate for you. And the top brands of the 4G USB Modems are HUAWEI and ZTE in China, Novatel Wireless and Sierra Wireless in USA, Option in USA, Alcatel-Lucent, Motorola,  LG in Korea also has 4G USB Modem, Pantech in USA is also well known.

 

At this time, you may feel tired, oh my god, so many options, hard to choose. Yes, there is easy way, follow your SIM card provider and find the unlocked model in the market. Take Telstra 4G LTE Aircard 320u (produced by SIERRA Wireless) as example, if you like it and don’t want to use with contract, you find online store selling unlocked one. Then you are fulfilled.

 

The premise is that you know this model number, but if you don’t know the model number, how to proceed?

So if you don’t know the brand and provider model, you can follow below steps to determine:

  1. First, confirm your local 4G LTE Frequency band, if you don’t know, please refer to below the two links:

A.)  List_of_LTE_networks: http://en.wikipedia.org/wiki/List_of_LTE_networks (check LTE Bands)

B.)  4G Map: http://ltemaps.org/home/  (check LTE network bands and status)

(Note: most of the information from the two links are right, but not all)

  1. After confirmation，you must make sure the local 4g LTE network is already launched to commerce. If not, there is no 4G network available there.
  2. Choose the right 4G USB modem which would work for this band. Here we have one option for you: 4G Mobile Broadband Shopping Mall (www.4gltemall.com )

To make it clear, here is another example to explain. Supposing you are living in Sweden, after check, we found the LTE frequency bands as below:

  1. Band 7 (2600 MHz) Deployed by Telenor/ Tele2 / Net4Mobility / TeliaSonera
  2. Band 20 (800 MHz) Deployed by TeliaSonera
  3. Band 8 (900 MHz) Deployed by Telenor/ Tele2 / Net4Mobility

So you can choose any 4G USB Modem that can work for LTE FDD 2600Mhz. And to use TeliaSonera, the modem must support 800Mhz if don’t support 2600Mhz. From this point, you can find that Samsung has two 4G LTE Surfstick named GT-B3730 and GT-B3740. GT-B3730 works on 4G FDD 2600Mhz and 3g 2100Mhz while GT-B3740 only works on 4G FDD 800Mhz, no 3G. So if you like Samsung, you may check whether the two 4G Modem works in your country.

You can check there are many models on 4G Mobile Broadband Shopping Mall that can work for this band, such as  ZTE MF820, HUAWEI E392, E398, SIERRA Wireless 320U etc…

 

And please confirm the the band is LTE TDD or FDD, because there may be TDD 2600Mhz. It’s special band for TD-LTE network, FDD 2600Mhz modem can’t work on this.

It’s clear now. But if your 4G Network is WiMax, there is few options now. We suggest you follow your provider now, perhaps in near future, you can follow my method to choose what you like. Good luck.